The 2880 with the firmware update is solid for being a slave, the only thing is as a slave of course the octave down button won't work. If I slow down my Boss 670 it follows it though.
From the update PDF:
"When the 2880 has EXT. CLOCK enabled and is therefore the MIDI Clock slave to another device, a fix has been made when Quantize mode is ON. If your MIDI master is continually sending MIDI Clock with MIDI Song Position Pointer data, the 2880 will read the MIDI SPP data and always start recording its loop on beat 1, as long as Quantize is set to on. It will also always end the loop recording on beat 1 of a bar so that the loop lengths are always x number of bars in length. This allows the user to more easily make loops that will be in sync with their MIDI master. "