Pros: The pro's are in the majority with this item, I'll sum them up:
- Sturdy build quality
- Very functional for it's price
- It works!

Cons: There are however some cons:
- It isn't based on a real ELM327 chip, but it's an imitation that emulates that chip (Hence the low price)
- It is very poorly documented, luckily, there is a lot of info available if you just google "ELM237".
- It isn't always easy to get it to work. I've spent about 8 hours trying to get it to work. I tried it on 3 different laptops, and it didn't work out of the box on any of them. In the end however, I managed to gather all the info necessary to tweak the settings, system and drivers to get it going, and now it works like a charm.
- Depending on where you live, you might get it cheaper on ebay.

Other Thoughts:

Bottomline: In the end, as always, you get what you pay for. The device does work, but you have to be prepared to put some time and effort in it.
If your a rather novice with computers and cars, I would suggest you go for a more expensive tool from a specialised reseller, where you pay more, but get support.