I use a mattock also (for dealing with roots and rocks in hardpan), but I see another advantage to this sort of slide hammer tool. Not only is the mattock very demanding of my physical energy and puts a lot of wear on my back, but it's also imprecise. I mean accuracy of placement. If you want to make your cut with any precision on placement... well, you can come reasonably close swinging one of those things early on in the session, but after an hour or so of swinging, I find I'm not very precise. In contrast, a shovel blade with a slide hammer looks as though you could be reasonably precise. (And around figs, I'd like to be precise... I've never used the mattock close to anything I wanted to keep... just for clearing out garbage trees and shrubs, when I wanted to get rid of them).
Seems like a very nice idea James. I hope the repair/refinement you're making works out well. Good luck (and I'm looking forward to hearing the outcome next week).
Mike central NY state, zone 5
p.s. I also sometimes use a 16 pound Pinch Point bar for similar work. (Or a 12 pounder for lighter work). It's more accurate than the mattock, but similarly demanding of my back. Also, the tip tends to blunt more quickly (maybe it's cheaper, less durable steel), so more time on the grinder.