there is lots of personal preferences including bevel angles (base and side)
the detuning past the contact areas is to reduce the liklihood of catching the edges and wiping out... usually good for noobie boaders...
down to preferences.
the file on the edge tuners is there to quickly remove material, but it leaves some its own small burrs and rough finish.
THis is where a say, using diamond stones comes in handy to polish (has to be a wet polish) base and side edges to be nice and sharp.
Are there better guides to buy? Of course, if you want to dish out the money
Burton grinds their edges to be 1° base bevel and 89° edge bevel (so it's at 1° setting on my base/edge tuning tool)