The cost of a device that reads your OBD2 codes alone is $100. The SG and UG can do this and much more. I'd go for the UG between the 2.
If you have an Android though, I would buy an ELM237 and pair it with your phone.
I bought this for $13, and it is full-featured, including the ability to read OBD2 codes and reset the check engine light.
Mini ELM327 Bluetooth OBD2 Auto Diagnostics Scanner w Power Switch for Android | eBay