I could never get WUD to work, it always shows many images out of date on my setup even though they're kept up to date by watchtower.
I just use watchtower, no webUI because it automatically updates everything nightly. The downside is obviously sometimes stuff breaks, but it's pretty rare.
You could also try portainer, it can show which stacks have out of date images, but it doesn't have an easy one-click update button.