Been following this since it started and decided that i would take a chance and risk my 3.55 CFW kmeaw ps3 trying 4.21 Rogero CFW and about ten mins ago it was a sucess and is now working great!
My PS3 is CECH-2103A (came with 3.40 so was never downgreaded, was a out the box right to 3.55 Kmeaw). ive had no problems at all so far but saying that all ive done so far is run MM and try loading Dishonored (which installed fine and is sitting on the title screen as i write this lol).
What i did:
1. Remove all my 3.55 games
2. Boot into recovery mode
3. installed rogero 4.21