just wanted to post my experience with this new cfw. i have a slim ps3 with qa flagging.
was on 4.21 DEX, downgraded to 3.55 DEX (using downgrade), installed 3.55 DEX (to be safe), reinstalled my CEX flash dump using mm CEX to get back to original targetID, installed kmeaw 3.55 (cex), then installed rogero 4.21 cfw. the two games i've tested (borderlands 2 & civilization revolution) work perfectly off of ext. USB hdd using the latest mm cex.