Can't say re: chess mentor but the turn-based ratings here are absurd I'm 2120 here and would be lucky to be 1800 USCF.
Rating equivalents?

Yeah you can compare them - the Glicko system used here results in way higher ratings than in USCF - there probably isn't an exact conversion formula possible (esp for all rating classes) but the Glicko ratings here are inflated by 200-300 pts easily over the equivalent USCF rating ie 2100 here = 1800 or 1900 USCF, tops - IMHO (just ask anyone familiar with chess.com AND USCF ratings)
I figure they use the Glicko system here so that boneheads like myself can believe or pretend that they're really way better than they are
The ratings on chess mentor are ridiculous, about how far are they above a FIDE rating? 400 points or so?