I say - why not? Particularly for a user. A safe queen should have the pretty, fancy stuff. Or maybe one for special occasions. But a daily user works better with man-made materials. At least I don't feel as bad about using it.
Of course, I live in the desert. Humidity is usually 10 - 15% or so. When it gets over 20% the folks here whine. I have had wood scales shrink. I've noticed some movement of ivory scales. Bone or pearl are my favorites as they aren't as affected. Stag works too, if the scales are nicely matched. It's fairly stable as well.
G10 is the least hydroscopic of the man-made materials, so it's a great choice for the desert. Micarta is almost indestructible, although it will shrink in a dry climate. I've got one rag micarta folder and it's very cool! Jigged micarta looks great on a slip joint! Carbon fiber is OK, but not really suited for multi-blade traditional knife patterns.
Here's the breakdown of the custom slipjoints I currently own:
- ivory - 4
- bone - 21
- stag - 9
- micarta - 4
- G10 - 1
- pearl - 19
- carbon fiber - 2
All of the ones with man-made scales are single blade designs. In fact, I don't think I've ever seen a multi-blade that had man made scales. But I bet if Ken posted one for sale, it wouldn't last long!
As an example, here are two in jigged micarta. You can't tell me a multi-blade knife wouldn't look great with these handle scales!