First off, please note that there are two different Rokinon 16mm T2.2 lenses in the Canon EF mount. One, the CV16M-C, is a discontinued older version (but still available as "new" from some retailers) that does not have the hybrid aspherical element that the newer DS16M-C includes. Either lens is designed to be used on an APS-C camera, such as your 450D. Both lenses will mount on a FF Canon camera, but the image circle will not cover the entire sensor. The version with the hybrid elements is currently priced about $200 more than remaining stocks of the older version at retailers that still offer it new.
Now for a complete aside to discuss the word "hybrid" as used in the video: The mention of 'hybrid' in the video is used to describe a lens with cinema type interfaces and controls that has consumer quality "still" type glass and optical construction. Such lenses often "breathe" when focusing (the field of view expands or contracts as the focus distance changes - it's almost as if the fixed focal length lens is 'zooming' in or out slightly). Some will shift focus slightly when the aperture is changed. "Still" zoom lenses often shift focus as they are zoomed in or out. This is true of many fairly expensive still lenses as well as the lower priced ones. On the other hand, true "cinema" grade lenses demonstrate very little to no focus breathing or focus shift when changing the iris (aperture) or when zooming in or out. Such cinema lenses are much more expensive than even very high quality lenses made for shooting still images.
The Rokinon 16mm T2.2 is such a "hybrid" lens as described in the video. It's got pretty good glass, but it's nowhere near the same quality as true cinema grade lenses in terms of focus breathing or focus shift. But it has also got the control interfaces that serious video shooters desire - geared rings to control stepless apertures and focus via "video rigs."
Back to our regularly scheduled program: Rokinon uses the word "hybrid" in a different way when they describe one of the aspherical elements in the optical formula of the 16mm T2.2 as a 'hybrid aspherical element'.
From Wikipedia's Aspheric lens entry:
An aspheric lens or asphere is a lens whose surface profiles are not portions of a sphere or cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.
The asphere's more complex surface profile can reduce or eliminate spherical aberration and also reduce other optical aberrations such as astigmatism, compared to a simple lens. A single aspheric lens can often replace a much more complex multi-lens system. The resulting device is smaller and lighter, and sometimes cheaper than the multi-lens design.
Hybrid aspherical lenses combine the properties of refractive and diffractive lens elements in a single lens element. A single hybrid aspheric element may replace several discrete elements, including conventional aspheres, in an optical formula. Again, though the cost to make a single hybrid asphere may be higher than that of making a single more simple element, the reduction in the total number of elements required often saves manufacturing cost, materials cost, and can reduce the size/weight of a lens even as optical performance is improved.
The Rokinon 16mm f/2 is an APS-C or micro four-thirds only lens. Based on the block diagrams published by Rokinon, the optical formula is identical to the 16mm T2.2 version with the hybrid aspherical element for most mirrorless and micro 4/3 mounts, but not for the Canon EF, Nikon F, and Fuji X mounts¹.
Block diagram published by Rokinon for all versions of the 16mm T2.2
Block diagram published by Rokinon for Pentax K, Sony α, Sony E, Samsung NX, Canon M (EF-M), and Micro 4/3 versions of the 16mm f/2
Block diagram published by Rokinon for Canon (EF), Nikon AE (F), and Fuji X versions of the 16mm f/2
As can be seen by comparing the block diagrams, the use of a single hybrid aspherical lens element has allowed the reduction of the use of elements made from extra low dispersion glass from four elements to one. ED glass tends to be more expensive as a material than standard optical glass. Hybrid aspherical elements tend to cost more to create from the cheaper raw material. So the lens designers decided to exchange the material cost of three ED glass elements for the manufacturing cost of a single hybrid aspherical element.
Assuming the same optical formula, the main difference between the 16mm T2.2 and the 16mm f/2 is in the housing and the control interfaces. The DS16M-C, which we will refer to below as the "cine" lens, is made primarily for shooting video footage. The 16M-C is made primarily for shooting still images. The 16M-C is currently priced about $230 less than the DS16M-C. We'll call the 16mm f/2 the "stills" lens, even though it can also be used to shoot video. Being a manual only lens, though, shooting video with it would be problematic for anything that required changing the aperture or focus distance during a shot.
The aperture control for the cine lens is stepless. That means as the aperture (iris) control is rotated the aperture can be set at any value between the maximum T2.2 value and the minimum T22 value. There are no 'clicks' to indicate a particular f-stop or to hold the aperture ring at a specific f-stop. The aperture ring is similar to a manual focus ring on most lenses - you can turn it smoothly from one end to the other with no 'clicks' or 'stops'. You must use the index mark lined up with the printed scale on the side of the lens to select a specific aperture setting. There is a geared ring at the rear of the aperture ring for use with external 'video rigs.'
The "stills" lens has clicks at the "full" and "half" f-stop positions between f/2 and f/16. There is no half stop click between f/16 and f/22. According to Bryan Carnathan's review of the Samyang version of the same lens at The-Digital-Picture, the aperture ring of the "stills' version can be left in between clicks. There is no geared ring for attaching to external rigs. (Samyang makes lenses that are marketed by resellers as Rokinon/Bower/Walimex/Falcon/Albinar/Opteka/Quantaray/Bell & Howell/whatever else they're calling it this week.)
The focusing control is also different between the two lenses. Both are fully manual focus only. The "stills" lens has a fairly wide rubber focusing ring but no geared ring. The "cine" version has a plain plastic surface that includes a narrow geared ring that can be used with optional external focusing rigs to enable more precise focusing control.
The older CV16M-C lacks the hybrid aspherical element but has all of the control features of the DS16M-C. The hybrid aspherical element gives a little better optical performance on the edges and in the corners than the older lens without it.
¹Note: The description of the "stills" 16mm f/2 at Rokinon's U.S. website is a little unclear as to whether it includes the hybrid aspherical element or not. The text description only says it has two aspherical elements. The block diagram indicates it is the same as the block diagram shown for the DS16M-C when no specific mount is selected. If one selects the Fuji X, Canon (EF), or Nikon AE (F) mounts the block diagram changes to a different formula. Selecting the Pentax K, Sony α, Samsung NX, Sony E, Micro 4/3, or Canon M mounts shows the same block diagram as the DS16 that has the hybrid aspherical element. Based on prices for the different mounts it's hard to see a big difference between the Canon (EF) mount, along with the Fuji X and Nikon mounts, which may be the older optical formula, and the other mounts which appear to be the newer formula.