I've used a few clone j heads in the past and as long as you set them up right they are o.k. The main issue with the ones I have tried is that they don't have the lock nut holding the PTFE liner tight to the aluminium part. I solved this by cutting a 6mm piece of 8mm OD, 5mm ID aluminium tube and putting it on top of the liner. The pneumatic connector then presses against this when tightened and, therefore, also keeps the liner tight against the block. If the liner moves away from the block PLA will pool in the gap and as soon as the hotend cools you have a clog. This maybe what's happened in your case
Andy
Andy