Used it several times for low-end and mid-range hotels. Often the cheapest deals on the interwebs. I think I've always taken a pay-at-the-hotel type of arrangement, so the risk is pretty much zero. If you're thinking that something is too good to be true, post it here so that we can all jump in!

One word of warning - Once Rakuten has your email address, they'll send lots of unwanted marketing emails, points updates, special offers and the like.