i did try using the twa with garageband live loops, with the loop recording function. yes, it works great & i had lot of fun. it takes some time to actually believe that backing drum loops are playing through your acoustic guitar, but once u get over that - creativity just keeps flowing. it makes u think a little differently from regular fingerstyle guitaring, the loopy nature sends your playing down a slightly different, but rewarding path. (for example, i started creating all kinds of hip hop grooves on ac gtr as i started playing over the hip hop template loops in garageband)

SO i can say that the twa works great with looper in iOS. to add to dave's comments : " I've used live looping through apps a few times, but without a controller of sorts, it kind of defeats the purpose " . 

Triggering the recorded loops on the ipad is possible through a dedicated midi foot controller like the behringer fcb. U can connect it into the ipad using the camera connection kit so that garageband receives midi messages (loop play, loop record etc).

In garageband, since u pre-set the number of bars(2,4,8 etc) u want to record for a loop(it even supports odd time signatures !) it automatically starts looping once u finish recording.