In before comments that "it sucks"...
Note the commuter in the second video who seems to understand what "vaktrak" means, looking down at the track after it passed to see if it actually did anything
For comparison, here's the old VakTrak:
Ignore the title above--this is the old Vaktrak, seemingly doing actual vaccuuming. The vacuum car is the two-axle car in the center of the consist, bracketed by collection cars fore and aft.
Supposedly NYCTA crews had to resort to in-house rebuilding to make these original units somewhat useful after critical components wore out or broke down without available replacements. The old units are also self-propelled, as opposed to the new ones, which depend on a work diesel for movement.