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.
Ben