Pros: Fairly light weight.
Hold securely, depending on the bottle, even mounted under the tube.
Unusual design.

Cons: Thinner bottles can deform and pop out if mounted under the downtube. (I use a velcro strap around the 2nd bottle because of this.)

Recommendation: I initially got the first cage based on the neat look, and the fact that they were cheaper than everything else the LBS had at the time. Pleased enough that I picked up a 2nd to go under. Easy in/out, secure hold on the top bottle, pretty good hold underneath.
At 10 bucks, it's a pretty good value for a nice lightweight cage.