I've been painting from my iPad since 2012. I've used my Soltek easel as a holder, I've attached it to my easel with clamps, and I've set it beside my work on my Hughes easel.
Caddie Buddy and I
learned about it from Jude Galbraith. It works great. I have it
attached to an old, lightweight camera tripod. The painting I'm working on is the one I started in the workshop a couple weeks ago. See the progress of "September Afternoon" below.