I have a Progressive PT50X 50amp and it works just fine from a 30 amp source or my Predator 3500 generator. I have also had to use it at Campgrounds that only had 30 amp hookups by using the provided 50 to 30 amp adapter from Progressive.
I prefer to have the portable unit because I can check the power before parking at a campsite, plus if something does go wrong with the unit it won't stink up the RV with smoke.
This is my second unit from Progressive. My first one had the cord come loose from the plug. It still worked OK but it was hanging from the wires and not the cord. Progressive replaced it within 7 days from the time I submitted a warranty claim...great customer service.