i've been using the hk one for a long time.
the interior construction isn't too bad, the balance area is the only thing that bugs me. lines of tiny smd resistors and no active cooling. the rest is solidly made and i've never had a problem with the charger. the 4mm jacks are big chunks of brass soldered to the board. there are better ways to do this, but this is a unit built down to a price. many of the parts are through hole, so if something does pop (the caps on chinese stuff are always low quality) and that makes it easy to replace things, even for beginners.
the other one in my stable is the accucell 6. i've got a dc supply in the house and then some large batteries in the pickup, so being dc only doesn't bother me. it uses a larger smd resistor gang on the balance side. a fan is placed right over it. i do like the layout of the accucell more than the b6ac in general, just seems like more time went into it and seems a bit more high quality.
both chargers feature a more or less standard way of doing the right angle riser balance board (without a connector that is). the riser board is soldered to the main board. basically they cut the boards to interlock and then ran solder on some exposed ground plane. effective, but not very tough. again, never personally had a problem with this method, and any fault can easily be touched up with a soldering iron. as long as you're not forcing plugs hard into it or ripping them out, should last a good long time, i've been using the b6ac for years and still works every time i plug it in, no fuss, all function.
ideally, i'd like to see heat sinks with a fan blowing heat out of the case on the balance area, the bleeder resistors used to balance out the pack or dicharge it are the main worry. that's where you're going to see the biggest heat spikes and sinking that out would up the life of the unit.
