I used that exact setup on my cab, 2 u360s for players 1 and two and two Magsticks (for 3 and 4).
The magsticks definitely feel more like arcade sticks, but I love the u360s for their flexibility. You give up a little in feel but you get a lot in flexibility to use them in different ways.
And with the mapping, I honestly haven't really noticed issues with 4/8/2 way restrictions. But that say, my hi scores are shamefully low,
so hardcore gamers would likely disagree with me.
About the USB though. I've got A LOT of devices working through usb and it has definitely NOT been without problems. I don't believe it's any one vendor's fault or anything, but it can get very tricky once you get past 4-6 usb devices. You got to pay attention to hub chaining length, the current draw of each device, the max amps deliverable to each hub via it's powersupply, etc.
I constantly have my u360s go "offline", as if they were unplugged. Oddly, that never happens to either of my Happ trackballs or my Logitech flightstick. I'm not saying it's the u360s fault, I'm just not sure where the problem is. Things will work fine after boot up, but if I let the machine just sit, eventually, I'll start loosing devices.
I also occasionally get "delays" with the u360s, I can open up the game controllers panel and start wiggling the sticks, and from time to time, the little X on screen that tracks the sticks placement will just stick in place for about a half second. Again, I suspect it's some peculiar combination of hubs, the way I have them chained, other devices I've got installed etc, but it's been maddening to hunt down. Just FYI.