The only time I've had problems with them was with a .25LA I've had on a couple of SPADs. The plastic backplate/needle valve holder kept breaking during minor crashes/hard landings and I'd have to spend $6 on a new one. I have since stopped crashing with that particular engine and haven't had to use the three spare backplates I bought.

I do get pretty nervous adjusting the high speed needle on my Super Tigres. They are very close to the prop. I agree that the angled HSN on the new AX is the best solution.