I have one that I got from amazon for around $65 last year and I agree with what was said so far, it's awesome. Personally I have it on my 10/22 take down and just got a second which is going to go on my 9mm ar then if I can find one a Sig MPX. The size of the dot is perfect for precision but not too small and very crisp. I have been very pleasantly surprised by it's performance.
I got one, and love it. Wait, there are two... never mind, I've got three if I counted right.
On on a shotgun, one on the PS90, and the third sits on an AK. They all get used regularly and none have failed yet.
All mine were purchased before the new ones with the included riser, so I can't really speak to how useful it is, but a test fitting at the LGS gave me the impression the Burris riser was just a bit too tall. I'd go with a UTG for such a low impact item.
If I remember correctly--
High mount (25mm) for lower 1/3 co-witness
Med mount (21mm) for absolute co-witness
Low mount (13mm) for ...mmm... other stuff.