I don't know why you guys recommend o-rings, the OP never mentioned anything regarding noise.
As for typing feel, I find o-ring reduce the travel distance and makes typing feel really weird. Not a fan of it personally. Unless the intent is for reducing key travel so you type "faster", in that case I'd say get a scissor switch and save yourself some money.
But from what I've gathered the OP just want different choices for typing other than MX Blue isn't it?
Orings makes the landing very different. and reduced travel distance is a "technical" plus.. because it makes timing control easier when you're playing the typing games.
ALSO, i believe most people are doing O-rings "WRONG" and the 40a is still MUCH too hard.
I use the silicone rings I cut from silicone rubber dome keyboards. They're around 20-30a, they return that walkin' on sunshine feel of bottoming out a rubber dome, which takes away the harshness of Cherry MX landing.
a. Shore 20A = Rubber Band
b. Shore 40A = Pencil Eraser
c. Shore 60A = Car Tire Tread
d. Shore 70A* = Running Shoe Sole
e. Shore 80A = Leather Belt
f. Shore 100A = Shopping Cart Wheel