If you want nice, bright, original arcade style concave pushbuttons in red, in a form that you won't need to mess around with, then the Red NovaGems will make you happy. These will give you a far deeper and more intense red illumination than using only one leg of an RGB drive with an EI button, and will be 5x brighter than a HAPP translucent with a ButtonBlaster (or any other standard "superbright") installed. And yes, the diffuser discs are recommended for buttons which you don't intend to use PGI's with.
As for the earlier mention of an EI button sticking down, the only thing I can imagine was the case here is that the RGB drive wasn't installed correctly. If it's at any sort of angle, then it's possible for the plunger arm to get caught on the RGB Drive PCB. Simply changing to a Micro-leaf switch wouldn't affect this, so I am at a loss as to how this might have fixed the problem.
The normal HAPP buttons are nylon, while the EI buttons are a much harder, more durable material that is better in many ways. It is far more scratch resistant than the softer nylon buttons, but the material is also not as "dead" when it comes to the vibration of the spring. If a quieter, stiffer button is your thing, adding a 1/4" to the length of the spring with a little stretch will tighten them right up and eliminate the spring vibration.
And yes, some of the EI nuts are a little tight, but you need not fear stripping anything. Just tighten them down as hard as you need to. They won't budge afterwards. And as was mentioned, don't mix up the nuts intended for the EI buttons with those used for the normal buttons. They aren't the same.
RandyT