The blade segment at the tip of the Stewart MacDonald Refret Saw cuts on the pull stroke, while the second segment nearer the handle cuts on the push stroke, so the natural tendency to lift the handle on the pull stroke (to start the saw on the 'back' tooth) and to allow it to drop on the push stroke (starts the 'back' teeth) keeps the unused blade segment out of the finish. It's easy enough to grind off one set or the other if desired, but in use, I have not seen much of an issue.
If you spend as much time as I have the past few years crawling through web sites and looking closely at any and all shop shots, you will have noticed that most repair shops have an array of guards to protect the top from damage during repair. Fret slot cleaners and saws jump out of fret slots, just as bridge slotting saws and files do on the bridge. One repair-generated ding on an instrument can erase any potential revenue - let alone profit - on a job, so the time spent fabricating guards is repaid many times over on avoiding repairs. Needless to say, avoiding damage to the shop's reputation is every bit as important!
If working the fret slots over the body, the bare minimum in this shop is a cork-backed piece of high pressure laminate butted up against the fretboard, or - where the extension is very, very thin, some 24 gauge (0.020") aluminum sheet backed with heavy gauge (0.010?) plastic laminating film.
The other repair people here will likely have some photos handy of these guards and top protectors, and I would certainly enjoy seeing what others use for the job.
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