ZH1-M is, like most astromech droids, highly idiosyncratic. The particular idiosyncrasy is this case is a seeming inability to leave anything at factory settings. Such modifications generally leave things working better than normal, so this might be seen as a good thing, but for two complications. First, once ZH1-M modifies something, it becomes difficult for anyone else to work on it; the settings just don't make sense to other mechanics. Second, ZH1-M becomes territorial about the modified devices, and stubbornly opposes returning them to the quartermaster or letting anyone else handle them in the first place. As such, Squadron Command has learned to be very careful about what they let ZH1-M work on. At the same time, this trait has forestalled any memory wipes, as Command does not want to have to go through the trouble of undoing ZH1-M's work in order to make the equipment usable again.
Not much is known about ZH1-M's construction. It clearly isn't a stock model astromech, though it may have been a factory second model or scrap built from astromech parts. For its part, ZH1-M claims to belong to itself, but doesn't clarify whether it was "emancipated" by its previous owner or just decided it belonged to itself after self-modification. Regardless, it takes orders just fine so long as one respects its idiosyncrasies.
Modification: ZH1-M loves fiddling with tech, believing that no tool or device is ever finished, and can always be improved upon or repurposed in some way. This is also a way in which ZH1-M acquires a feeling of ownership over things.
Placard Hunter (0): ZH1-M is fully on board with Camanis's ace-hunting ambitions, seeing them as a way to raise the profile of its work and open up wiggle room for further modifications.
ZH1-M is a chrome astromech droid, lacking in any cosmetic flourishes. It's vocoder is pitched lower than most droids of its types, giving it a more ornery than usual tone.