I've never held the MR-350 in my hands, and I don't know if it is any larger than the BU-353. If it does have a larger antenna than it BU-353, then it could be better. If the size of the antenna is the same, then performance-wise both of the units should be identical.
MR-350 is attached to quite a long 15 feet of cable which ends with a PS/2 plug. You need to use also either a USB or an RS-323 adapter (sold separately).
BU-353 comes with the usual 5 feet of cable. The cable ends with a USB connector which plugs directly to your laptop.