That is a great question!
As with any update (WordPress, plugins and themes), adoption the following good practices is wise:
1. Testing these updates on a testing/staging server before rolling them out on your live site.
2. Making sure you have a complete database backup before you update anything.
That being said, our current recommendation is that our customers remain on the highest WooCommerce 2.x version since WooCommerce 3 has introduced significant changes.
With that in mind, we are currently running extensive tests with WooCommerce 3 to ensure a smooth experience for our Event Tickets Plus users.
Stay tuned!