Dont bother, they go thru blades pretty quick anyhow, and are SO easy to slice your face to bits. Just get a normal razor with replacable bits, not like you will save a massive amount of cash.

Main tip is be careful as fuck, use them at a shallow angle, and press gently.
I been using one for years (not totally, just to get bits of my over-complex sideys right ) and i still cut myself sometimes.