I like keybr! The only thing that bothers me about it is that many of the words are made up, which means I have to think more about individual letters than I usually would. On the flip side, it does help you directly address your weak spots.

Another tool I like is https://10fastfingers.com/typing-test/english. It's simple and enables you to practice for 1 minute at a time. Sometimes I'll do it while I'm waiting for people to show up to a meeting