Overall its a pretty good product for the price. Its more than powerful enough to cut things like fibreglass, carbon fibre, concrete etc.
There are a couple of design flaws such as the button to remove the lock on bits requires quite a bit of force to engage so you an loosen it. The power switch is also located in a stupid position - once this thing is on, Its on and you have to adjust your hand position to turn it off. In that sense its actually a pretty dangerous tool because if you loose control of it, it could remain on and hurt you. The extension device also doesn't work very well in that its not suitable for high powered tasks. But that could be due to user error. Finally, replacing the sanding bits is extremely difficult and could easily have been made easier. I had to cut the rubber head down to fit new bits on. Again this could just be down to user error.