I have an M42 mount Helios lens that I want to use on a Minolta AF mount body. I've found this adapter online but wanted to verify it is the correct adapter before I purchased it. The lens is a Helios 44M-2 and the body is a Minolta 300si.
by my best knowledge, this is the right adapter.
the flange focal length (FFL) is the value you need to adapt to use the lens on a given camera. The Minolta FFL (44.50 mm) is pretty average for standard 35mm cameras (which is why their lenses are so to canon cameras for example). Luckily, the FFL of the M42 mount is about a millimeter longer (45.46 mm), which leaves exactly this mm for an adaption of the mounting mechanism. https://en.wikipedia.org/wiki/Flange_focal_distance
This fits quite well with the visible dimensions of the adapter you posted. The description says it does exactly what you want.
Be aware, you won't have any autofocus.
If you want manual focus anyway, get a cheap minolta from the pre-autofocus era, with a fixed focal lenght Minolta lens (eg. 50mm/1.7). You can get them for less than 30$ in north America and Europe, and if you don't specifically go for the look of the Helios, will give you better image quality. If you want to go with the Helios, you could buy a Praktika or something comparable for even less money, which fits the Helios natively.