Better yet, you'll get a free week when you sign up, so you can give it a go and make sure you're going to use it before you decide to pay for it.
The #NintendoSwitchOnline paid membership service will start on 19/09. You can sign-up for a 7-day free trial from Nintendo #eShop at launch! We will introduce more information during the #NintendoDirect on 13/09.— Nintendo UK (@NintendoUK) September 12, 2018
If you do decide to stump up the cash, it'll set you back £3.49 a month, or £17.99 if you go for a full year straight from the off. Which isn't bad, all told.
We'll find out more info about Switch Online in the rescheduled Direct tomorrow night. Hopefully they'll finally announce that they're getting rid of the stupid seperate mobile app...