I started using bass shakers over 10 years ago, and while my current theater doesn't have them installed, I do have them ready to go for if my financial situation turns around and I can get on the new seating for my home theater.
Let me put it this way, they are a great effect, but are by no means a replacement for a poor or non-existent subwoofer. I know that you are looking to keep volume levels down, so they might work for you. Heck, they are advertised to add bass feel when you don't have the gear to pump the bass, or for when you need to keep levels low (apartment).
Here is a link to my REALLY old home theater that I first put bass shakers in. It will give you some info as to my start with them and what other people thought, but again, they are more of a supplement to bass than a replacement.
Nick's Theater V1.0
