Yes, there were two competing vendors and they were paid for with DOT funds.
I believe Garett made four and GE (Budd) made four. The two sets were not compatable and had significant differences. They all looked similar to M-1's with different details. They had the two tone "M" logos with a Federal or DOT logo on the end doors and the sides.
For a few weeks one set made regular trips to Greenport in overnight testing. They were horribly noisy, sounding like a 747 at takeoff. You'd watch the lights go on in the farm houses enroute as you passed. They used trememdous amounts of fuel -- kerosene, as I recall and they stunk up the entire North Fork. I had the opportunity to operate one of them and they had M-1 type controls, but with a weard turbine-induced lag to the throttle response.
They had to be compatable with low level platforms, and each vendor came up with its own solution. One had a "trap door" in the vestibule that slid open to reveal stairs. Anyone on the trap door would fall out.
The other had folding stairs that dropped down under your feet -- another unnerving option.
As Otto said, they had cool roll signs; I'm lucky enough to have grabbed one off the Garett set before they were scrapped.
The GE set was converted for MetroNorth into M-1's (maybe M-3's?) by the Long Island Rail Road in Hillside Shops. They are probably still running today. The Garrett sets had "drop in" turbines that took a substantial part of the car and were deemed too much trouble to convert to electric.
Before those cars came, the LIRR had another experimental turbine car they kept in a shed on the old wye in Ronkonkoma. That was also a DOT funded project that, I believe was made from a converted Budd coach in the early 1970's.