I think a few of the existing resources on this website will already answer most of your questions. For example:
I believe the above questions answered all of these:
- Does all filters that match the Cokin holder will fit in the lee holder?
- Assuming that the answer to the first question is yes I would like to get a recommendation for a good solid ND set of filters (1,2 and 3 stops).
- Does lee's ND filters worth the high price?
- Is there any other cheaper set of ND filters that can produce similar results (in terms of quality)?
The next question is:
- What are the differences between lee's polyester, resin and glass filters?
This is answered by Googleing the exact same question, which leads us to this article at the Lee website:
LEE Resin filters are individually hand made, the 2mm Optical Resin is cast in our factory, hand dyed and cut to give a very high quality product both in colour accuracy and optical quality. They are hard wearing and ideal for use on location. Polyester Filters are made on a master roll, the colour being coated onto the surface of the clear polyester base material. Because the filters are very thin (0.1mm) the optical quality is high. Polyester is a good, low cost alternative to Resin, but because of the manufacturing process polyester grads are not available. The Glass Filters that LEE offer tend to be specialist filters that are not available in other materials, such as the enhancer or polariser. They are hard wearing and scratch resistant but tend to be expensive. Do not drop!
That leaves us with one final question:
- I would like to know what am I losing by selecting a different manufacturer.
Lee filters are highly regarded for multiple reasons, and understanding those reasons will help one to understand why different brands are a tradeoff.
Lee filters are handmade, requiring up to an hour of highly skilled labor to create. This hands on approach allows the process to be more closely monitored and adjusted as the filter is created. If you are interested in the exact process that is taken on to create a Lee filter, I would watch this short 15min video for a great overview of the process: Mike Browne visits Lee Filters(YouTube).
Lee filters are known to have very little color cast. When using Neutral Density filters, color cast is typically your enemy, especially with long exposures. While Lee filters do not always eliminate it(especially when considering 10 stop varieties), they are widely regarded to have among the least amount of color cast in their filters among competing products.
Lee filters are made of resin. Why is resin better? Because it allows for sharper images, especially if it is a thin resin and you are comparing this to glass. Resin can be optically more pure than glass. Yes they can be easily damaged, but that is the trade off that you get for the sharper image that some desire. Note - Lee does offer a "Pro Glass Series" if you prefer that route.
I also believe that part of the reason that Lee filters have been so successful and highly regarded is that the mounting system, Lee Foundations Kit is also of very high quality and functions very well. Having both the mounting hardware and filters from one manufacturer does assist in the consumer's perception of quality in a brand name, and in this case I believe the perception is reality.
Lee filters essentially give you the highest quality glass/resin available, thinner and more optically pure than competing products. It has one of the best mounting systems available to match it as well.
Is Lee worth the "high" price? Well for those that desire or need the best quality, of course it is. That is why they are in high demand and often purchased and used by photographers. Is it worth it for you? I can't decide that. Other options such as Singh-Ray, B+W, Schneider, and even HiTech, Tiffen, and Marumi can offer other options that aren't Lee. But you will find time and time again that people love Lee filters. Personally, I use HiTech and B+W and am very happy, but this is just one of many trade offs I make in photography as a hobby.