Phil's decompressor does look a lot like a hummingbird skeleton. If any of it comes apart, the engine damage is going to be extreme. Ive not read of this happening though?
The thing seems to work on and on like the rest of the bike.
I do like the simplicity of the in head decompressors.
On the other hand, I purchased a new Ossa Trials bike in 1974 and had one of these simple poppet type decompressors fitted to be used as an engine brake. They are very effective when sliding down a mountainside. The rear wheel gives good braking but still rotates just enough to keep you upright.
The decompressor was fitted by Dave Wildman himself, the Ossa/Triumph dealer and Westwood racer.
It came apart on the second day of use, destroyed the piston!
So maybe the hummingbird skeleton is OK.
Glen