It's worth it if you transact enough money to make it worth it. If you're just using it for zaps, it's kinda hard to justify the monthly 21k sats. Most people don't zap 21k in a month. So you're paying more for the privilege of zapping with Alby than the total amount of sats you're transacting.

Don't get me wrong, Alby is an amazing platform that provides a ton of features, and a great user experience with the monthly subscription, but I think you have to look at your monthly transaction volume and weigh that against the premium for using the platform to determine if it's a reasonable expense.