I haven't. However I just pulled up all the MJ items and I'm impressed. Only one of them bothers me. The rest look correct. They also have PSA/JSA/Beckett on all the MJ's. So at least it seems they are trying to get them authenticated by the more reputable cert providers.
I am assuming that this is the company you are talking about? When I google High End Memorabilia - it links to this company: http://www.sportscollectibles.com/high_end_gallery_c48395.htm; (just so we're talking about the same place? - you didn't include a link)
They've been discussed here previously. I hadn't heard of them before, but they seem to be offering items from the notorious Antiquities. It looks like a disastrous auction.
If you are talking about Sportscollectibles.com all the music stuff I saw on there looked authentic -- but those prices! Over 3 grand for a Michael Jackson signed photo and over 7 grand for a Thriller?! Stay far away.