Basic charger
Often charges cells in pairs or simple groups. Fine for casual use; weaker at spotting one bad cell in a pair.
Independent-channel charger
Monitors each slot separately. Better when you mix cells of different ages or residual charge.
Smart charger
Detects charge state and uses a proper termination method rather than a blind timer. Prefer this over overnight “dumb” chargers for NiMH.
Charger-analyzer
Can discharge, measure capacity, refresh, or cycle. Useful if you maintain a set of NiMH for devices that officially support them.
Still not a reason to use NiMH in an alkaline-only device.
Safety basics
Charge NiMH in a charger designed for NiMH. Do not put disposable alkaline or CR coin cells in a charger.
Charge on a hard, non-flammable surface; stop if a cell gets abnormally hot.