OBD2 adapter to use with Forscan

[NZ XR6]

The check engine light on the MB came on for the first time recently. Topping up the coolant fixed it - it came on after I parked across a slope, and the coolant level was just above the MIN line.

Anyway, I've been meaning to buy an adapter for some time and will go ahead and do so. A couple of questions first:

• Are the Bluetooth adapters reliable, or is it better to buy a USB version and use a laptop?
• There are some cheap adapters on eBay, or is it better to spend the extra on a OBDLink device. The EX would be under NZ$100 from the US.