what about galaga?
There is no natural inclination to push up or down in Galaga. Thus no need for the restrictor. I have played tons of Galaga, using 2-ways, 4-ways, and 8-ways and it is always the same.
But, in Defender, there is a strong inclination to push left and right on the stick in an attempt to make your ship go left and right. The first time I ever saw those restictors I thought of Defender.
Actually, there are a few other games that would benefit.
Asteroids (and other left-right-thrust games), if played with the joystick rather than buttons, then these games would benefit from the restrictor.
That Space Invaders clone where you control a missile cart, and the button is a thrust button.
I DO want a 2-way restrictor, but unfortunatley I use Wico sticks and not Happ ones, and thus can't use Oscars.