Hi!

The more expensive (non-clones) are usually better in construction, and have been tested properly - with the clones commonly found on ebay/amazon, they are cheap, but you do run the risk of getting a 'not very good' one.

The clones can manifest issues in a variety of ways if you have a bad one:

* Frequent bluetooth disconnects (though this can also be caused by an android bug in some older handsets as well)

* Pauses in data communication (common to quite a few clones)

* Incorrect data being requested (again, this is common and Torque will warn if it sees this happening a lot)

* Working on some manufacturers protocols, but not others (a famous example would be not working on Fords J1850-PWM protocol due to a PCB design mistake, but working on other manufacturers protocols (CANBUS, ISO9141, etc)

* Working one day, then the bluetooth radio ceases to function and you can no longer pair do it

* Always requesting a PIN number when you powerdown the adapter and power it back up (though a similar issue exists in recent samsung phones that a workaround was recently created for)

Now, that aside you can get good clones that function at a reasonable speed

The best I have seen is the OBDLink MX from scantool.net - it's had a lot of work put into the bluetooth speed side of things, and has been tested thoroughly. Hence the price 🙂 but to put it into perspective, on a mercedes (which uses CANBUS 11/500k) I have been getting nearly 100PIDs/second read speed where as the clones can only get about 26 to 35 (depending on the adapter and phone used)
(tests were done on a Merc CLS320 using CANBUS 11/500k, and a nexus 4 with OBDLink MX, and several clones)

In short, the clones work, but if you want something faster that's not going to give any grief, then consider the more expensive adapters.

Theres a list on http://torque-bhp.com/wiki/Bluetooth_Adapters which are made by several different peopel