OH man, this is some nerdy and obscure stuff, but since you asked . . . .
The numbers really just refer to the differences in the levers. From my experience and what I’ve read, the HS22’s have a 2mm larger piston than the HS33’s and flow more fluid so they can effectively push the brake pads a little longer distance when you pull the lever. How much you will notice this difference is not really clear and I haven’t ever measured the difference myself.
The HS22 larger piston is good for folks that prefer to ride with the pads away from the rim a little more. The HS22 lever is great for 36"er wheels, where wheel flex can cause nusiance brake pad rubbing under acceleration or idling. HS22 levers haven’t been made for a while now.
The HS33s are still made, but the newer style lever just doesn’t feel right in your hand. Not sure why. Now, the older style pre-2005 discontinued lever is what I have and is better for unicycle riding IMHO. The 33’s have a red adjustment wheel on the lever blade to adjust “on the fly” the distance between the pads and the rim, a useful feature if you damage a wheel riding off road and need to continue riding with out having to pull out the hex-wrench to manually adjust the brake pads back from your now out of true wheel. The HS33 lever body is slightly smaller and the lever blade is usually a little shorter compared to the HS22. Both kinds of brake lever ends can be cut off with a saw if they are too long. HS22 and HS33 lever blades are not interchangeable.
I have heard but not verified that the KH spooner will only fit on the HS33 lever blade end, which is more knifelike thant the HS22 ball-end set-up.
Both types use the exact same wheel cylinders, fittings tubing and hardware . . . the parts shown in the pic. I posted yesterday.
Any other Maggie rim brake-techies out there that can add to this description??
B