They have obvious aesthetic appeal but wood holds moisture and it does not take much to get sucked into lens elements under the right conditions. Ditto for wood finishes or other applied coatings. The best cap for a lens is hard plastic that cannot bend to protect its surfaces and is a stable material. I spent some time with a professional lens technician last weekend that advised that I acquire desiccant when working in humid climates to combat the issues with humidity. I left him a marvelous 203mm Ektar that was suffering the effects of hazing initiated from some moisture that got into the lens elements. Just something to consider.