this is a controversial opinion: auto-menders aren't very good

[Sundance]

I agree, auto-menders do trivialise medicine, Worst offender here is synthflesh auto-menders.

I don't see how patches require skill. And I'm pretty sure menders waste far more reagents, though we can always make them slower and more wasteful.
(Also unlike patches menders require both parties to stand still so they're unusable in combat / when fleeing.)

This is the solution, I think. Making them dump far more of their chems would make these more niche in there usage. Perhaps also lowering their internal size by a few units too? So they'd have to be refilled sooner also. Strike a balance between its internal storage and its wastefulness and I think it might be more balanced.

Now you'll need to be far more resourceful with your use. Maybe you'll need to order more chems from QM or whip that pharmacy into shape. 

In either scenario you'll be left with a device that will heal really good, but will run out really quickly. You'll want to save it perhaps for a more dire scenario. Maybe you'll opt for something else in the meantime... perhaps a patch?

This also would also not affect borgs, for to heal; a borgs function is attempt to do better than that of its fleshling counterpart.