A few things to note...
A Wico 8way leaf stick wont be good for games like street fighter.
A square restricted joystick like the Happs Comps are much better for that.
Wico leafs have a round edge.. and in Rortron, you tend to walk continuously from one direction to the next... so this helps very much. If they joy has a squared edge, your stick gets kinda stuck in the corners... and prevents smooth fast transitional movements.
The wico leafs are very touchy... so they can be bad for fighters... where you must for example jump diagonally all the sudden. Or stop moving then start again. They also require cleaning and adjustments on occasion.
The 4ways have a diamond shaped restrictor edge. So, in Pacman, when you are going to turn a corner, your stick may go from Down to Left in a straight diagonal path. On an 8way stick, your stick might go from Down to DownLeft to Left. And.. the path wouldnt be a smooth guided shortcut regardless. The diamond shape really changes the feel of the game. Makes it easier to control on games like Pacman... and much more pleasant and fun experience.
A u360 with a circular restriction may play better than a standard 8way... but still wont compare to a real wico leaf set. Not sure if you have to keep the circular restriction on or take it off to play other games. I know if would make streetfighter games a lot more difficult to find diagonals, with it on.
So I always wondered if Robotron (dedicated) had angles not emulated in MAME, guess not correct?
The original game is replicated correctly in mame. There are no additional angles. This adds to the challenge greatly... which makes it one of the most kick butt games of all time.
FYI, Robotron uses wico 8way leaf joysticks, not 4ways. Wico made both, as well as microswitch balltops.
You can usually find a few on ebay here and there. You might find a decent one on a used control panel of a different game. They are getting harder and harder to come by. Also, you have to be carful not to buy the knock-offs. Supposedly a chinese company made a replica... but messed some things up, and they dont play the same as a real wico.