sound integrity

After a friend used Sound Integrity subs in his home theater system (2 - 24") and the sound floored me by the clean, ultra wide band and accuracy of them, visiting the site I was looking at the amplifiers, components and SQI subwoofers. I watched reviews and dynos on them. They seem clean...

I was looking for a new budget build sub and stumbled on a Stereo Integrity HT 18" sub perfect for my budget. I just don't know anything about them. Any info on build quality, performance, sound, etc. will be much appreciated.