It depends what you want to do with the subwoofer. If you just want to have louder booming bass and aren't bothered about integrating the subs with the mains or the room then they are good value subwoofers by home audio standards. If you want decent quality bass and cleaned up mains then you need the sub to return a high passed signal to the amp and to include a way to specify the gain and time delay with frequency. Alternatively you can do this with an upstream box of electronics like a PC, minidsp, probably some AVR receivers, etc... and supply a low passed signal to the sub with whatever controls it has got set to off.
There are similar studio subwoofers around the BK price point and they will likely offer a filtered return signal to the amplifier enabling better integration with the mains. Looks will be poor though. Price would need to be raised to get adequate gain and delay control.