Figured it was time for an update. I've been using U-40 now for over two months and still no signs of yellowing, and I don't think it's going to yellow anytime soon (if it ever does). Here's what I've noticed about U-40 and Flex Coat:
For those of you that didn't see the first part of this review: Trondak U-40 LS Supreme High Build Review
Trondak U-40 LS Supreme High Build:
1. Somewhat slicker to touch than Flex Coat
2. More durable (U-40 can tear if you get a hook point or other sharp object through it, but it doesn't chip or crack)
3. More teeth-resistant than Flex Coat. U-40 doesn't scratch as easily or as deeply, mainly due to its extra flexibility
4. Cheaper than Flex Coat
U-40 is also considerably thicker than Flex Coat, but that can be either an advantage or a disadvantage. This probably wouldn't be an issue if you used the medium-viscosity version of U-40.
Flex Coat Ultra V:
1. Easier to mix bubble-free than U-40. I can mix Flex Coat completely bubble-free, which so far I haven't been able to do with U-40.
2. Slightly longer cure time, which means you have more application time.
3. Less odor (U-40 doesn't smell very much, but Flex Coat has practically no odor at all)
4. Easier application. Flex Coat is thinner and spreads easier than U-40.
Those are the main points I can think of, but that should give a pretty fair idea of how U-40 compares to Flex Coat. Neither of these can claim the title of the "Perfect Topcoat", but both are excellent coatings that provide very good protection for lures.
Thanks for reading.