Good inertia triggers are pretty good, and most of the ones on decent guns are good. However, there's no getting around the issues that a light load might not reset the trigger, or if you don't get the gun properly against your shoulder, it might not reset. And you are indeed at a loss if you have a misfire. First one is more likely to happen if you're fooling around with real light loads while shooting targets, second more likely to happen when you're hunting and make a bad mount, third can happen any time and can happen with factory ammo, although probably more likely with reloads.

The vast majority of the doubles I've owned have had the correct number of triggers: 2. However, I've had all of the above happen to me--not all that often, I'll admit--and I've seen all of the above happen to other shooters. I wouldn't necessarily reject a gun because it had a single inertia trigger, but if I were to choose, I'd go DT first, mechanical ST second, inertia last.