I've never done the double-wide action, but from those who have there's at least one drawback.  Every time your partner rolls over, you get a cold draft.

If you're only occasionally going to be tripping together, get matching bags with the L/R zip.

Regarding BA systems, I'm going to switch to it for next year.  I've used their insulated air core pad and it's the most comfortable pad I've ever used.  Their system makes a whole lot of sense to me, why have 1/3 of the bag's insulation be useless weight & volume.  Also, I'm a tosser & turner in bed so their system makes even more sense for me.

I've never heard a bad review of Big Agnes gear or their service.