i had a Minuteman Port-a-scrub, same machine. it's mainly a hard floor machine. it can be used for agitating carpet, but the rubber barrel that picks up the water from hard floors can get lint stuck on the squeegee bar and cause streaking.
I'd look at that 13" scrubber from Jim England. he's offering 15% off machines. the offer is in the swapmeet room.
You are correct that the Minuteman version of that machine has a small spray nozzle. The stock Sprint machine originally came with too small of an orifice too. However we made a revision to the Sprint models so they can now spray out enough detergent.