The only train manufacturer building DMUs in America today that is Buy America compliant is Stadler Rail in Salt Lake City.
Their FLIRT train has "alternate" FRA compliance. Worldwide, Stadler has sold over 1,500 trains (as of June 2018)
Presently Trinity Metro runs them on their TexRail service, operating it on shared tracks with freight trains using a time separation schedule but will operated them with FRA compliant passenger trains over the share tracks without locking out turnouts. It shares tracks with the Trinity Railway Express (TRE) FRA compliant trains in Fort Worth/ But it has built flyovers to avoid busy freight train tracks where time separation schedule could not work. And while Amtrak trains also visit downtown Fort Worth, the Amtrak trains and TexRail trains do not share the same tracks. With different floor heights between the various trains, the platforms height need to be different, hence using different tracks. DART plans to use the same trains with its Silver LIne, and so will the Arrow trains in the Inland Empire in Southern California with just two cars per train. Additionally, the last FLIRT trains being delivered to Arrow will have hydrogen capability in the power unit instead of diesel engines.
The DMU version of the FLIRT train can be a 2, 3, or 4 car version with a power unit installed between two of the cars in for all practical purposed permanently coupled or attached train set. the UK's Class 755 trains are very similar, the Class 745 is a 10 car EMU trainset without a diesel power unit. The DMU Class 745 trains run just like an EMU under a catenary. The East Anglia service thought they could easily separate the 10 car train set into two 5 car train sets for maintenance, but changes their opinion quickly after trying. They enlarged their maintenance building eventually to accommodate all 10 cars.
I'm not that familiar with MBTA commuter services where a DMU might make sense. But anytime you run short passenger trains on freight lines, careful attention is needed for proper shunting of any wayside signals. DCTA and CapMetro run 1 car Stadler GTWs, and both had shunting problems activating Various wayside signals correctly. But they are the masters of the railroad being used, so after significant effort they have been able to fix the shunting problem issues. That is something most freight operators will not do, they will instead insist upon a minimum number of axels in a train to ensure proper shunting of signals. So, short DMU trains in my humble opinion will only work on rail corridors owned by the transit agency providing the service. And at best, coupling two DMU trains together you could end up with an 8 car train set running in a multiple unit set.
https://en.wikipedia.org/wiki/Silver_Li ... d_Transit)
Countries where Stadler has sold FLIRT trains to include: Algeria, Azerbaijan, Belarus, Canada, Czech Republic, Estonia, Finland, Germany, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Serbia, Slovenia, Sweden, Switzerland, United Kingdom, United States.
Although DMU and H powered versions are fairly recent.