i had one fitted on the old engine when i had the carbs put on but it started to play up and wouldn't let me go past 70mph (not that i wanted to officer).
I had one on my type4 until recently. I think they are a good idea if driving these old vans is a new experience. You are unlikely to ever hit the limit if you have any respect for your engine. Mine used to cut in at about 57mph in third
Always had one ,never any probs , can't see how they can play up, surely they either limit it or not? 5400 rpm don't get reached much
Serves no purpose whatsoever, and introduces another potential point of failure. If you're above 5400rpm, you'll be dodging lumps of aluminium/magnesium, so you'll know anyway.
Either way, given that the aircoolers are low revvers, I can't see they serve much purpose, apart from introducing something else that could pack up...