I am a real believer in tankettes for garrisons these days
I mean if you have them via old models or captured equipment, you might as well put them to some kind of use.
But I can't imagine producing them is a favorable tradeoff compared to just using cav otherwise. Garrison casualties are trivial if you either a) use collaboration or b) the area doesn't have much/any industry so you just set it to local police force and ignore it.
I don't have NSB, so maybe you can make absolute garbage with very low production cost + high hardness that's cost-competitive enough to be viable (edit: it seems so per above). I can't imagine it's making a big difference compared to just slapping cavalry though. I guess it depends how much resistance you usually get like you say, but w/o NSB it's hard to justify.