I have one, running my Galaxy 88, 939, Superstar 400, plus a mobile eq and a large amp on my 10" Cerwin Vegas... granted, the stereo isn't on while the Superstar is, but still... I bought the Powermax on recommendation from on here. I want to say it was Redbeard that convinced me. I do not regret it one bit.
An I'm considering ordering nuther'n. Always need a backup. If my converter currently installed running camper fails, one of these doubles the converter in place.