Haven't used a JB3 but can answer the MT side:
- You can go mic in with no preamp no problem on the MT, 1/8" or TRS.
- Battery life on the MT depends on the card you use and the mics. 4-5 hours is pushing it with a CF, 3 with phantom power or a microdrive.
- I'd go with the JB3 if you're just using it as a bit bucket, the MT if you want more flexibility in a smaller form factor.
- Don't forget to factor the cost of a CF card into the price of the MT.
If you can get an MT for the same price as a JB3 you're either getting ripped off on the price of the JB3 or the MT is hot.
Craig