Yeah, I find they work better than some of the paid IR's I have, though that depends on the tone I'm aiming for.
For example:
- Sneap Edge or Any of the Guitar Hacks impulses seem to work best for a good Mesa style Rhythm guitar tone and occasionally leads as well. Especially Low tuned or darker material Like Modern Metalcore, Djent or Groove Metal.
- Mesa Traditional, OS and the Engl impulses work really well for everything above and in-between. The Fender And Marshal tones are also great for leads, cleans and brighter rhythm tones.
Additional free impulses I have found useful include the Devils Lab impulses which can definitely work for deathcore and harsher tones, the Aris effects pack which is a great starting point for Modern Metal guitar tones, and the Wilkenson Audio impulses which work great for all kinds of mesa tones.
That's how I use them anyway.