Re: 5D3: are there any "issues" with this camera?
 

No, the profiles are made and installed through the Canon software. So your warranty is fine. You can also make your own custom profiles and install them as well. This is the best way to the "look" you want out of the camera.

Re: 5D3: are there any "issues" with this camera?
 

Technicolor worked with Canon to develop Cinestyle. They used some proprietary Canon tools, so Cinestyle is able to do some things that isn't available to those of us using the standard profile editor. (I believe that their main "trick" is to lift the blacks. h.264 is known to be noisy near it's floor, so they avoid that area.)

Re: 5D3: are there any "issues" with this camera?
 

No ... not for loading in CineStyle. Programs like Magic Lantern that can have an effect on the actual OSX "may" void the warranty. People are free to create whatever profiles they like. That's why the Canon Utility allows you to install CineStyle and other profiles. It's totally safe and way better than the standard profiles in my opinion. Some people use the stock Neutral profile with the following settings: Sharp = 0; Contrast = -3; Saturation = -2; Color Tone = 0) and then correct in post, but I like CineStyle because of greater dynamic range. Check out below here what I was able to do to the smoke by using CineStyle. You could not do that with a Standard Canon profile without introducing weird artifacts. However, with that being said, you will need to make your clips come alive in post with proper color correction/grading and sharping (usually around 2.5-5.0 tops in FCPX or 80% in Pr). Hope this helps.

Re: 5D3: are there any "issues" with this camera?
 

The problem with Cinestyle is that loses 16 levels (out of 255) because it lifts the blacks up that much. It will also increase noise in the shadows and decrease the level of midtones.

Try the Flaat10p profile. Way better.