I own the Boss RC20XL and really like it. It is great for practice but I use it at times during performance with the band. One song we have plays an 8th note repeatedly, and lightly, through the entire song so I get that going and then go on playing the rest of the song. Mostly, I use it for practicing lead parts and scales.
The down side is that at times the Boss pedal seems to have a mind of its own. I press the switch for recording and all the sudden it starts playing a recorded loop that I made months ago. Not sure what I am doing wrong but I am pretty sure its my fault.