OK, plastidip update. I finished painting my wheel and let it dry. It looked amazing - ly AWFUL! The colour in the above photo looks alright, quite nice even, but in the light of day I think the use of 'Gunmetal grey' is far from the truth. It looks more like primer. Think battleship grey. I'd used plenty of coats, so it wasn't the thickness that was the issue, the colour in the above photo is nothing like the finished product.
Needless to say, after a test fit to the car, just to see A) how my new wheels looked regarding fitment/offset and; B ) for curiosity to see how awful the primer grey wheels would look on the car I began the 'easy, just peel it off' process, glad that I hadn't actually painted the wheel in 'real' paint.
So, can you just peel Plastidip off? Yes and no. If the Plastidip is applied liberally (i.e. thick) to a flat, smooth surface, yes, it just comes straight off. BUT, it the coats aren't really thick (but still thick enough to be the same uniform colour) then you need to pick at it. Also, if the surface isn't flat (for example in my wheel where the Torx bolts are) then it's a real PITA. It can be removed though by rubbing with your thumb/finger - just expect sore thumbs afterwards.
Credit where credit is due, it is easy to use and can be removed easily if applied thickly to the right surface. I imagine the black stuff that members use for their front bumper lower lip is brilliant. But please don't buy the gunmetal grey unless you want what ever you're painting to look like it's been prepped in primer awaiting paint.