I have the Legacy 500, I didn't read the specs before buying, but the price was too good to pass up.
The power rating was a bit of a surprise, however, I've found that it is way louder than similarly rated amps.
I put it up against a well known class D amp rated 500w at 4 ohms through a 4 ohm 4x10, and the GK's 300w at 4 ohms was significantly louder and had way more to give too.
GK rate their specs at 1% THD which I believe is about as honest as this stuff gets these days. I expect most class D amps are rated at higher THD meaning that their useful output will be smaller...