We are currently using a Fletcher mount cutter with a moveable cutting arm on a backboard. Having issues as follows: over and undercuts, wonky down cut in first 2-3 cm, not getting offcuts square using steel edge ruler and stanley before mount cutting!

We cut single, double and multi mounts (did a 12 apperture yesterday) but are having to throw lots of mounts away because they're wobbly or the mount board wasn't square in the first place. This is making us very slow. Having identified mount cutting as our biggest problem we want to upgrade our mount cutter, the sooner the better, but don't know what to go for. We are cutting A0 mountboard and want something that can cut mountboard down to size as well as bevel cut. If we could cut backboard as well that would be great.
We would really appreciate some advise on what mount cutter to buy. Digital seems unnecessary, so I guess we're looking at a good quality professional hand cutter. Thank you.