I read an article about them awhile back. Supposedly they are very similar to Priceline as far as getting access to the undersold hotel rooms, but unlike Priceline, they got around the "not disclosing" the hotel name requirement by only supplying the prices via SMS, Facebook app and one other similar platform vs over the phone/web. I've used them a few times now and have had very positive experiences.

Some things that I noticed:

1. If you click the back button after clicking on a hotel that you're interested in, it seems to always deduct another $1.
2. If you search too often in a short period of time the prices will likely increase
3. It's really tough to get an agent early in the mornings for late check-out, but they are great about getting you upgraded for free in the afternoons/early evenings if you request an "agent" through the SMS text.
4. Not all of their prices are the cheapest...sometimes cheaptickets with a promo code or one of the other booking companies will still be better, but for the most part it does seem to be cheaper, sometimes even over 1/2 off. We got a beautiful suite with Hyatt recently for a fantastic price. It seemed to get cheaper from about 3pm on until we booked around 6pm.