twice the the things can go wrong with two engines. So, are two really more reliable than one, ore do you double your chances of not getting to fly if you have to keep two engines running...
This is true even in full-scale; owners moving to twins from singles don't think of the double-trouble factor at first. Also, it's the old saw, "The remaining engine takes you to the scene of the crash." With center-line thrust setups like you'll have, single-engine ops are much easier but still not fool-proof.