I've had the Gametel Android Controller for about four weeks now, so I think I can give an objective overview of its pro's and con's.
In essence, the Gametel Controller does exactly what it is designed for. It lets you play games on your smart phone in a much more pleasant way than by using the virtual keypad on your phones' screen. The controller's keypad works quite well, and the buttons you push are directly translated to actions on the screen, so there are no delays or whatsoever. I did find that sometimes the diagonal directions are not correctly registrated, so your game character will move to the right/left or squat. But that's a minor issue.
Contrary to the virtual keypad on your phone, you can actually hold a button while pressing another one. For instance, while playing Megaman, you can charge your weapon while jumping or running. With the virtual keypad, this is not possible. Regarding phone type, I have a HTC Desire and a friend of mine a Samsung Galaxy II, and both were attached on the Gametel without problems. A phone that is wider that the Samsung Galaxy II won't fit, because the Galaxy II just fits to the attach point of the Gametel (it's a clamp).
The Gametel is quite light, but having a phone connected to it does not outbalance the whole. So while holding it, you won't have the feeling that the phone/Gametel will fall out of your hands because the top part (phone) is heavier than the lower part (the Controller).
There are however some minor issues: first of all, when initally establishing the Bluetooth connection, I was unable to connect to the Gametel Controller using the prescribed method in the manual. I had to go the Bluetooth connection options of my phone and manually link the Controller to my phone to overcome this problem. Also, the buttons are quite small (smaller than for instance the NES or SNES gamepad buttons), so it happens that I push two buttons at the same time which results in undesired results. Another thing is sometimes the bluetooth connection repeatedly breaks up, which basically halts your gaming as you can no longer move your character. I think this is related to the battery of the Gametel Controller being almost empty, but I am not sure given that there is no way to see how much battery life you have left. Also, there is no charger included in your package, so you have to use your mobile phone charger. I found this quite annoying, because it happens that both your phone and your Gametel Controller are empty and thus, you have to charge them one after another. Given the high price (approx. 50 euros), I would have expected a charger included in the package as well. Lastly, I am not quite convinced of the build quality of the Gametel. It feels like a plastic toy and I am afraid it won't withstand more than a year of hard abuse. The clamp holding the phone seems to be the weakest link, as it is controlled by a simple spring. If this one snaps, you'll be left withouh means of connecting you phone to your Controller.
Desite these minor issues, the gamepad works almost flawlessly and is certainly a major improvement when compared to the virtual keypad of your phone. But 50 euros is too much, 25 would be more appropiate given the build quality and small flaws.