I just received the unit this afternoon. Since I'm in the US at the moment, my use was only running a few tests with a spare prepaid TMobile SIM.

The first thing I should say is that it works. I can make and receive calls over it without a problem. I haven't bothered with data. The calls are clear and it works very similarly to the factory Apple dialer app. In bound calls can be answered outside the locked screen even when the password is on, but while this is going on there is a security vulnerability. You can hit the home button twice and access any other open program. If you switch over while the phone is ringing, the phone will not relock. This however, assumes that the thief has stolen both your iPhone and your GMate. As long as you keep the two in separate places, this doesn't seem to be much of a real world threat. At the same time, I'd hate to make this argument to an IT Department.

The device is very small and light. Inside my jeans, I barely feel it. When your phone is bonded with GMate, you seem to lose the ability to have a bluetooth connection with your handsfree.

All and all, my opinion is fairly favorable, but it is not been subject to real world testing.