Quick on. Quick off. No hunting for alignment. Satisfyingly positive feedback. Save time when changing lenses. The only other one I would consider is one that is made of soft plastic and slides on without twisting. But still Pentax brand Rear Lens Caps work best. I replace the Rear Lens Caps that come with non-Pentax lenses with Pentax Rear Lens Caps.
Pentax Lens Cap Rear for Pentax 645 and 645N Cameras is available at Microglobe at discounted price. Microglobe is largest online sport optics store of the UK.
Stevenson says that the idea for the holder came to him after he lost his camera's lens cap while at the hospital to witness the birth of his daughter. Four prototypes later and the mechanical engineer's patent-pending plastic lens cap holder is ready for commercial production. As I write, his has reached its funding target and production is scheduled to start within the next couple of weeks, with shipping promised a few week after.
Pentax rear lens cap for K-mount lenses. Designed to fit more tightly than the Pentax caps, especially on 3rd party lenses. These caps are also about 20% shorter but wide enough to seal against the o-rings on weather resistant lenses.