I know that there are several reputable sellers that sell on that site. I have never ordered off of it, but I think you'll be fine. A lot of sellers on there also list on eBay.
Never have used it, but did see Facebook posts from Seattle Orchids a while back saying they were using it... so, I suppose that like ebay, depends on the seller. I should browse around sometime
I bought two plants on that web site (from the same vendor) over the summer. Plants were fine and vendor was helpfull, but compared with Ebay the web site itself was a bear to navigate - in particular to do one transaction for two plants.
I got so disgusted that I asked them to delete me, once I settled with the vendor.
I also have the feeling that very few people look at that web site, as many nice plants never receive a bid.