If you only need it for 1 night, it can be a decent deal - if you get a good price.
I wanted to extend 1 night, and was told I would get the same price online, but that I should pay in person, instead of doing it online.
Well, when it came time to pay, I think I ended up paying quite a bit over what the online price was. I think the guy was playing some sort of game and capitalizing on customer / foreign ignorance.
Another guy in my room had the exact same thing happen, and felt like he got taken for some extra money, too. They might also be playing tricks so they can make you check out, then come back - and they try and charge luggage storage fee.
So if you're thinking about staying 2 nights, you might be better off just booking 2 online. It's a good deal if you can get a cheap rate, but I don't really trust the place to sneak in some higher prices......