If it's the same one I got that was on offer a while ago, don't bother! Switches itself on randomly and doesn't actually work, I couldn't even be bothered to send it back.
If it's of any interest, Silverline do a digital angle finder for around £20. I have a couple and they're darned accurate. Just as good as my £280 Winkelfix.
I've had one for over a year and it's been very reliable. Mine lives under the mitre saw, it makes setting angles a doddle. I have a nice reference square to check / zero the rule against.