I like, and use, the blue because you don't have to heat it up if you want to undo what you tightened down. It can be removed with hand tools and a little pressure.
With the red, it sets up solid, but you usually have to heat the surface to undo it.
While that may be okay for some applications, there are parts of a firearm that sometimes you would prefer not to risk tempering and changing the color just to undo something.
On your own firearms, that might not be a concern, when you are doing work on someone else's firearm, well, I would prefer not to risk it. You know?