Ok... During the month in which I had the RC-20XL, I used it extensively for practise and gigs. There is no delay between the end of your 1st loop and play back. The RC50, however, does. This is because it quantises the three phrases together. There's a patch you can download to allow you to switch between rhythm priority (causing the delay on the 1st loop you record) or sound priority. With sound priority your loop will be flawless, but if you use a rhythm guide - it'll automatically revert to rhythm guide, because well...it needs to.
www.myspace.com/kevcooke listen to Sky High on there
www.isound.com/kev_cooke then on here.
The recording on myspace was done using the RC-20XL and the recording on iSound with the RC50. The sound quality of the RC50 is significantly better.
As for ease of use with the RC50, it's just a case of actually reading the manual, and practising with it for a while. It's got so many features, to expect to be able to just plug in and know where everything is and what it does is just unreasonable I think. Once YOU know what you're doing, it's quite easy to use.