Portable is the key to me, i travel a lot because of my job so you can imagine.
The MBR is really amazing, i've been using Roland/Boss for years so it feels like home to me since i have it, the interface is easy to understand and there is enough buttons to have the important things at your fingers.
I use the machines this way: guitar plugged to MBR guitar input and Palm with Bhajis loops to the aux in.
When i have a guitar idea just put a simple pattern running in BL or sometimes i came up with a BL idea and add guitars, then i record all togheter like a little clip.
Just like a notes recorder, and when the song is in my mind i re-proggram the .bjm, render to wav, import to MBR and overdub all the tracks i need.
Sometimes i mix in the MBR or Reaper according to the number of tracks and my mood ;)
I could use the Live function like you said but i'm not into live performances now.