Hello. I have the Opus BT-C3400 and I can tell you that you can charge the Keeppower 16650 BUT it will only charge it to 4.2v.
What if you switch the internal switch to 4.35 volt?
The Opus charger is awesome and I chose that over the others (Maha, LaCrosse, etc) because it can charge Ni-MH, Li-Ion, LifePO4 AND when it's done charging... It does a trickle maintenance charge( around 24-34ma) on Ni-MH batteries to keep it full unlike others that cut off and the battery can self discharge sitting in the charger.
The trickle charge is bad for LSD cells like eneloop.
The Keeppower does have protection circuit however and it seems to only want to charge to around 4.30v before it kicks in and cuts off the charger. So it misses the mark by .05v.
The protection kicks in before the CV phase, this means you need to charge with a low charge current to get the most energy into the cell.