Imo if you are under 180lbs and not riding super aggressively you can probably get away with EXO+. 

But if you are above, or ride at an expert level do yourself a favour and get both an insert and the DD.

DD gives you both more cut protection, as well side wall support for cornering. Still not as much support as a dh casing and you can peel tires of the rim if your really given’er. Running a Cush core or a full size insert alleviates this, locking your bead in, and let’s you run pressures way lower than would normally be able to. This gives way more grip but also protects your rim. 

If you are thinking about it you might as well do both and then never think about it again.