I've heard mostly good things about the HF Predator, but when we were looking for a secondary genny to compliment our onboard Onan (way overkill for most uses) 5 years ago I went with a Champion 3100 inverter genny. The price for HF Predator 3500 you stated is pretty much every day pricing, can be had for under $700 on sale, black friday pricing would be a good time to acquire.
My specifics for our secondary genny were inverter type, capable of powering our AC unit, eco-mode, quieter, increased fuel efficiency, and most important was remote start mimicking our Onan's ease of startup/shutdown. Over 400 hours and 5 years later, it still runs like a, you guessed it, a champ. Customer service was great when we needed high elevation carb jet, had it on my doorstep 3 days later.
