My experiences with RJ on a series of flights (MAD-AMM, BCN-AMM, CDG-AMM, DME-AMM) in J on DONEx trips have been great. The hard product is good, seats are comfortable (although not lie flat for these legs), inflight entertainment is pleasant. For me the big plus was the food - they bring a range of foods to you on a table and serve you there - allows you to have a little bit of everything they offer if you want! Food is good, reportedly (from partner) they were good with talking about the wines on offer. I haven't failed to get one of those OWE personal greetings from the CSM when travelling J on RJ - and they were really very lovely.
I've at times also been the only person travelling in J at times, and they're awesomely attentive when this happens.
Overall, I really like them.