There are a few over 3.3 on the ESTAR product finder, and I think this is just a reflection that these products are new and there aren’t that many out there. It’s all a bit dumb since a 240V can be run in hybrid/high output/electric resistance mode and kill your efficiency, but the 120V are usually HP only and they have the exact same compressor since they only need like 800watts in HP mode, so there’s no reason for their efficiency to be lower whatsoever. Do what you need to do to get that incentive money though.
You also have to deal with a ton of extra plumbing and envelope penetrations, and the space the thermal solar collector takes up doesn’t fit nicely with a solar PV array either. A HPWH might use 800 kWh/year, so thats like less than two 400+ W panels to cover all your water heating. I think thermal solar is fine tech and there are certainly situations where it makes sense (perhaps yours) but overwhelmingly HPWH is more cost effective and simpler.