I’m not sure I’d say you couldn’t/shouldn’t use it in a 32gal.
I bought a used MP10 for a 57gal build that didn’t happen (ended up going big right from the start). While waiting on my new tank to get set up and cycle, I used that little MP10 in a 20L I used as a holding tank for some livestock I got a deal on. Worked like a charm.
Could I have blown all the coral and fish out of the tank?? Absolutely! But if you choose one of the more moderate wave patterns and keep it at the lower end of its capacity most of the time, I don’t see why you couldn’t use it in a 32g.
That said, I don’t think I’d pay full price for a new one if I was only going to use a fraction of its power and capabilities. You should be able to pick up a good used one pretty easily from someone moving up to a bigger tank that either doesn’t need it or can’t use it because the new tank’s glass is too thick (think it is ½” max for the MP10).