I think the main thing in Looper pedals are to have zero latency, two or three tracks, no drums, a way to record or pre-record for a live performance and a way to select the pre recordings bass on the song you want to play without necessarily having to play them in a certain sequence.
by the way. is there a pedal besides Looper that can be "trained" to play lower octave bass lines that follow your guitar chords. would be handy live for songs where the bass line follows the chord melody.

rr