Hey that's your prerogative, they do add more work because you have to take the wheels off to torque the spacers and you have to torque the spacers at least as often as the wheels get torqued. If you're used to running steel wheels and hubs then they need to be torqued more often, because the heat expansion on aluminum is higher. If you're used to aluminum wheels/hubs then it's the same.
But their safety is a simple matter of physics. As long as the material is correct and there's enough of it to support the studs, the adaptors are just as safe as running aluminum wheels or hubs as long as they're properly installed and maintained. It's just that simple.
Are there adapters out there made from inferior materials? Absolutely. But that's true for a lot of parts, you have to make sure that what you're running is up to the task. I've run adaptors, outside of an extra set of nuts to torque they're not an issue. Hell pretty much every dually truck runs them, and runs them in MUCH larger offsets than anything that would get used on an A-body.