If you install a responsive theme or mod, it's supposed to show the user the appropriate format for the device they're using. PC users will see pc view, mobile users will see mobile view, they cannot choose which view they see on their device. That's why it's called responsive, it automatically adjusts to viewing device. If we reinstall responsive Curve mod in Curve MC, mobile users see the mobile format. (I've done some tinkering with it and corrected the nav problem.) PC users will continue to see what they've been seeing all along, there won't be any change. The mod converts Curve MC from non-responsive to responsive. Mobile-desktop is a responsive theme, mobile format is built in.
From the many comments posted, it seems that most members have been very happy with Curve MC, whether using pc or mobile. If your major reason for going responsive is seo, I believe it's possible to show Google responsive Curve MC, while keeping everyone else on current non-responsive theme. We can have two versions, guests (and Google) see responsive, members don't unless they opt to select it in profile. Don't think it can be done in ACP, but a simple database edit should do it. I'll try it on test install soon as I get a chance.