I agree with Jo6pak. People who don't get to handle these firearms on a regular basis should be allowed the opportunity to appreciate the differences among all of these firearms, and really see what the designers had in mind. After all, they are paying for the experience, not just to throw lead downrange. A direct impingement M16A2, a roller-locked MP5 and a piston Kalashnikov all feel, sound and operate in a very different way and if I were paying my money, the fun would include being shown the differences.
Now, if you have two of something, that's a different story. Having an M16A1 or A2 and a fully decked out M4, complete with coffee maker, would be a great treat to show evolution of the system. My pre '86 M16 (I only own one full auto, and that's it) is usually set up M4-esque, and is very easy to keep on bowling pins and milk jugs on full auto with an Aimpoint M3. With zero magnification and both eyes open, it is very easy to just keep the little dot on the moving milk jug and keep it dancing on full auto.
I do think any optics with magnification would make for more frustration than benefit with novices. The restricted field of view would just remove much of the fun of the instant feedback from the target one normally gets from full-auto fun. You can always bring a scoped varmint gun to show off the fun of optics, just leave that stuff off the full autos.
If you want comfort, start them off with a .22lr upper on your M16. Full-auto .22lr is great to introduce the concept of trigger control on full-auto, without the intimidation and excessive muzzle rise of larger calibers. As to comfort on the other guns, part of what people who don't normally shoot full-auto will be paying for is to be taken outside their normal comfort zone. That's why roller-coasters are so popular.