First, the AT&T Unite Explore (Aka AC815S) only supports bands 2, 4, 5, 12, 17, 29 and 30 (our review: https://www.rvmobileinternet.com/gear/att-unite-explore/).
For minimum Verizon LTE support, you want support for at least 2, 4, 5, 13 and 66. Band 13 is critically important for Verizon, it's their long range band. But if your AT&T device is unlocked, it will work - you'll just be missing a huge chunk of Verizon's coverage across the nation.
Next, Visible is a smartphone plan and only authorized for use on smartphones, not mobile hotspots. While it does 'just work', they do have the right to block usage. And their hotspot usage is capped at 5 Mbps - which is plenty for most stuff on the web. They claim to expect only 480p (SD) video streaming on Visible.
- Cherie