If you know the area well, you can get a really great rate on a very nice hotel, but sometimes you get a so so place.
Here are two examples-
I don't know Denver very well, so I bid to be anywhere but downtown (they have sections you can choose) a 2 star at $25.00 a night and got Candlewood suites in an iffy area of town. It had a kitchenette and was fine, but not the absolute cleanest I ever stayed in.
I also bid on an area I knew well, West Dearborn MI and for $30.00 a night I got a Hyatt at the mall there, pretty swank digs.
You have to be ready for whatever you get. They charge your card and you get no choice in hotels, they just assign you one. There is also no refunds.
I have more good than bad experiences.
I have also found that the bigger the metro, the better the room, if you choose the upscale side of town. Start bidding low and choose higher star levels if you want only nice places. All they can say is no. The most I have ever paid is $35 a night, but I was willing to stay at a two star.