I'm not 100% familiar with the Oregon sharpener, but if you put a reversing switch on it, in addition to making sure the wheel is on tight, you might want to make sure you have another nut to act as a 'lock nut" on the shaft.
I toyed with reversing my grinder (Stihl USG I bought on ebay), but after I went to a diamond wheel and got it set up right, I didn't see much difference between the left and right hand cutters. Reversing would also mean I'd have to deal with spark shields etc.
I did rob a couple of ceramic magnets from a microwave magnetron - about a powerful as you can get, and free from any appliance repair depot! Just put one in a plastic bag where the sparks fly and it will trap most of the debris (with diamond you don't have to worry about the wheel dust, just the steel). To clean it, just peal off the plastic bag.