They are the work of the devil and your wheels are more likely to fall off.
Plus that method of centralising your wheel may seem like a work of pure genius, but it'll seem a lot dumber when you don't have the thread bar to fit the wheel up with at the side of a road, in the dark, when it's raining.
If you MUST run spacers then maybe think about fitting wheel studs and bolts, like proper cars run - put spacer on, put wheel on, easy.
They still introduce a world of bodging into your car that is totally unnecessary, with the right fitment wheels.