Our goal is to create a simple, reliable and easy to use device
A mains controller with built-in multimeter? That's not really a simple device - when or why would I want to use it? I have mains controllers that control mains well. I have (too many) multimeters that do multimetering very well. I can't envision a situation where it would be worth the time to take this out of its box for those features.
It sounds to me like you've made some mains monitoring thing and figured that the bit that measures the waveform could also be tapped into to provide low voltage input too, so you've added that because you could. But in doing so I think you are confusing the message of what this device is really about.
I would suggest that you forget the multimeter stuff. Sure, leave it in and it's a nice surprised to a purchaser, but that's all it is and shouldn't appear in the blurb. Making it a feature detracts from the more unusual features that are what will sell this. Concentrate instead on the mains waveform and power monitoring, and the relay stuff is a sub-feature of those.