I have what's left of an 8 lb jug of MRP that I bought at some vague point in the last 10 years. I tried it in a number of guns and never was quite happy enough. I never had a complete temp sensitivity disaster, but I don't load hot. But I did not get session to session accuracy retention that I would like.
IIRC, I read a LOT about temp sensitivity, as I hunt in Kansas, where it can be zero in deer season, and it might have been 95 when I developed my loads. MRP was reputed to be better than some of the Alliant powders (the old one's like RL-22) in terms of temp sens, but not as stable as the Hogdon temp stable series (H4350, H4831, H1000 etc)
There also were rumors that MRP was the SAME as RL-22. This is not likely true, but they are very similar powders in terms of burn rate and density.