I have 2 older SD tents (a Hyperlight 2 AST and a Velox 2) that I have kept on as car-camping tents. I think SD has always made quality gear (in terms of sewing, etc.) but has always been a little "off" on design. Most of their shelters are "almost perfect" with one or two features that never seem as good in practice as they probably did on paper. For example, the Hyperlight has a lot of floorspace, but is roughly diamond-shaped, forcing a little pad overlap in the foot area. I can't say that is true for the Mojo, but it is a generalization that fits.
I also can get a discount on a major-label gear manufacturer and this occasionally makes me buy gear that is great but not necessarily what I would buy if money didn't matter. It's a nice problem to have.
Can you buy a Mojo online from a shop where you can return it? Even if you're out some shipping costs, I'd want to test that design before committing to it as my primary shelter. If you are set on a free-standing shelter, the BA tents seems proven. Also, check out the REI Quarter Dome line. Amy Lauterbach (who posts here regularly and has done some amazing trekking around the world) uses an Quarter Dome REI 2. There's even a plus+ length version that might get you enough room to add your kid.