I felt compelled to respond because I live in Boston and I have a Unication G5.
As far as decoding and performing on P25 trunked systems, it is hands down the best. It easily outperforms my SDS100, 996, 496. It is also compact, sturdy, and rugged. I use it to monitor Cambridge and it works great. With that said, as pointed out earlier, it is a pager and not a scanner so functionality is a lot more limited than a scanner. There is no channel hold or lockout function, so prioritizing traffic or incidents is limited. You can, however, play around with your scan lists as a workaround (one for ATG, one for PD, FD, BAPERN, etc) which works fine. Boston isn't too heavy in P25 trunked yet, so I still use my 996XT most (even more than my SDS100, which I don't love). If I am traveling somewhere where P25 trunked is the standard, I always program and bring my G5. You will need a good understanding of trunked radios if you buy one and want to program it (unlike newer scanners which often with preprogrammed systems).
I think the key is that commercial grade radios that focus on one type of comms (i.e. P25) consistently outperform multiband scanners, IMHO. A Unication radio with some more scanner type functionality would be awesome, but my fear is that attempts to be more multifunctional will sacrifice performance. The reason the G5 is so good, is because it is commercial grade. Much better than a multiband scanner made of cheap plastic with poor reception and audio.
As for MSP, a G5 would probably only be useful right now in Western Mass as the new P25 system get built out, I don't believe they offer a model for analog trunked systems such as the MSP system still in use for most of the state.