The SMS-1 truly is a wonderful user-friendly product. I found that I get a different response at a lower volume level. This is something I'd never have realized had I not used the SMS-1. My solution will be to simply keep the level up!
Furthermore, I have been able to set my two subs up in stereo to be just about perfectly flat all the up to where I have them blend in with my mains [all of this is for 2-channel], and all using the subs' own on-board controls. I would have never figured this out without using the SMS-1's tone generator, microphone, and graphical display. Now, I don't even use the SMS-1's EQ functions! There's simply no need since I got it flat without it.
My point is that without the SMS-1, I'd never have gotten my dual sub set-up tuned this well. It is just an amazing tool, and well worth the investment.