I believe for the 18650's efest rates them at 35a continuous, but they are well know to overate their batteries. Most according to tests are only 20a continuous. I'm not sure about the 18500's.
I have flat tops of those same batteries. And, yes, consider them 20A. That's plenty for most of my builds.
The only atty I need 30A batteries for is the Aromamizer and its on a Sigelei 100W with two vtc4s.
I may still get a Gizmo someday. I've always liked it, and like the colors.