I don't want to single out this particular Homeplug for criticism, because all manufacturers do the same. They tout a headline theoretical speed limit which is really not achievable in real life. It's a bit like ISPs selling you an ADSL line that promises 24mbs, only to discover that you're getting just 6mbs.
Anyway, these are fast units but do not reach anything like the quoted 500mbs. The best I'm getting is 150mbs between two adjacent rooms. This isn't bad, but not as fast as I'd expect. Perhaps it's my wiring, but I find that with the previous models (AVLan 200) I was getting 100mbs. You would have thought that a pair of 500mbs units like these could achieve something a little faster than that.
Despite these lacklustre statistics, I've tried many different Homeplug manufacturers and Devolo remain my favourite in terms of reliability and ease of use.