Well, now they are!
There's the Mr Limpy XS, Small, Medium and Large.
The XS is PERFECT for my packing, while the Small doesn't actually fit as well as I'd like and I have to use a harness or packing briefs. The XS has larger balls which make the base against your skin (if packing in underpants) much sturdier. The bulge is more natural too.
With the Small, the balls are thin and the shaft dangles too far down and doesn't sit right in my pants. With a harness or packing briefs it is ok, but I really like the balls and the shape of the XS.
Now, the Medium and Large are a completely different situation entirely.
The Medium can fit into my pants well enough without a harness or briefs, which is great because it can't fit into my packing gear. It's too thick.
Same with the Large except the Large doesn't even fit into my pants. I hesitate to call it ridiculous because somebody out there might use it well, but it doesn't fit my harness and it doesn't fit my underpants so it's very hard for me to use.