At the risk of disagreeing with some, I admit to liking HP CombiPlan tanks for smaller volumes of 4x5. The only time when I had issues with sheets slipping was when I still had the unnecessary blue shims installed. As soon as I got rid of the blue shims (apparently included by mistake by the factory) even very vigorous 5 inversions across two planes in 5 seconds, every 30 sec, works well for me. Even tested violent shaking in all directions for 30s to 1min with HP5+ and FP4, successfully, though TMax 100 slipped a notch in that test. What helps is to make sure the retainer is on properly, not pressing on top of the sheets too hard, not loose either. I push it on, then relax it and let it find it's own position.
They are a bit slow to empty, 23 seconds, but I'm getting even development for 8+ mins dev durations. Get your hands on one before they disappear, as they have been, sadly, just discontinued... Alternatively, the Jobo Experts are super. And a new CPP-3 processor is on its way later this year, but at a price.