He found CH M1.1 lacking bass and not great match with R1 beryllium tweeter, too bright. Momentum is excellent but Mephisto has more drive and control.
Another friend have TAD E1 but have experience with R1. His favorite is Burmester 909. Same reasons compare to Momentum and ARC 750SE.
All comes down to system matching and personal taste. I don't have experience with Mephisto but Momentum is fantastic with Wilson Alexx, Sabrina and Alexia 2.
I may be the friend that King is writing about. I have the TAD Evolution system as can be seen in my signature and have been living with it for over 3 years. I consider myself immensely blessed.
On the R1, I've heard them many times at my dealers before he sold them off right before Covid. The best I heard them was with the M600 monos and they are able to control the speaker, especially the bass, in a very pleasant and sought after way and I though the system was really magic. Only got to hear that twice before the dealer rep took them back, but I thought they were really good. I have not compared them to my M2500, but think they are the next level up. I've also heard the R1s with D'Agostino momentum a lot and think it very good, but not on the level of the M600s with the matching preamp. Also heard with ARC 750SE, very nice but I preferred either the M600 or Momentum.
In regards to the Burmester 909, I heard it with my E-1s (that first/second/third demo convinced me and I purchased the E-1s a few months later) using a Burmester pre and phono pre and big Clear Audio table in an approximately $300k setup with Nordost Valhalla 2 and it was glorious. I don't have the room for that amp and it was not in my budget either. The M2500 was best to all other amps or integrated's I compared it to four years ago from Luxman, Pass, Burmester $25k integrated, and maybe another I forget.
Finally, don't be afraid of TAD Class D, for me it became the end of the road. I've heard A, A/B, D, etc. It plays with the best for sure.