I sell these Atrend DD/AQ boxes here at the shop.
They are great for entry level systems, but are tuned in the ~37hz range.
I usually only sell them w/ the DD500-series subs, or as 'out the door' boxes.
They are my go-to prebuit box if the customer does not have to budget for a custom box.
Build quality is pretty dam nice. They hold together very well, but the glue is kinda sloppy (over glued).
Some time $50 extra price for a custom box can make of break a full system sale, and I would MUCH rather put a customer in one of these Atrend boxes than see them go down the road and get a $60 Q-Power turd-box.