I subscribe for a month and say "OK Google, remind me to cancel (whatever) in 3 weeks." (and adjust the number of weeks depending on how many months). Haven't had a surprise bill... so far. I mean, I know it will likely happen at some point but has worked like a charm. It takes only a second and can be done by voice while you're using your hands to place the order for the trial, so I think that's why it works well. Of course, if you don't have a Google Home, doing this will be completely useless lol