First, I've never used the Kase system you linked. Take the rest with a pinch of salt.
I have a few magnetic filter rings in my drawer that I used only until I got annoyed by them (didn't take long)
It's a great idea that smacks of convenience and speed. However.
Mine were chinese imports (Xume I think) and relatively cheap compared to what you've posted. I seem to recall about £80ish for 3 or 4.
1. You need a ring for every filter. If you don't, you just spend the time unscrewing the magnetic ring instead of unscrewing the filter from a lens. You don't realise how often you need to swap stuff about until you're restricted. I needed one for each colour filter (red, orange, yellow), my cpl, an nd filter and the lens cap. Without a doubt, I'd leave it off the red filter, and that would be the one I'd choose to use. The kit you posted looks like it has 1 ring. Which would frustrate me no end.
2. The magnets I had were quite strong. This is a good thing because you don't want them falling off, but it's a bad thing because removing them requires a degree of force that, when you're trying to not muck up glass and thus hold things between two fingers, becomes almost as frustrating and twice as dangerous. I had one (fortunately cheap) filter fly out of my hands because of too much force and not enough grip.
3. You can't pick them apart with gloves on. Fingerless gloves or no gloves or maybe high quality leather ones. Wooly ones? Forget it.
In the end, I decided against them. Pain in the bum.
