As far as I know, no other manufacturer makes RPN calculators. I could be wrong, though. I own two 48GX, one 48G, one 48gII (its keypad is nasty), two 28S (the foldable ones) and a 42S. I also had a 48S, but it broke. Its ON-key stopped working. All too late I learned that it's a known contact issue between a couple of circuit boards—you need to lightly press down on the panel between the display and the B or C keys while pressing the ON-key! My 48G developed the same issue much later on, but luckily I found the solution before I simply threw it away! (There's stories of people fixing it by actually washing the calculator in water, or spraying ridiculous amounts of contact spray through it, but I'm not entirely certain those stories aren't made up!)
The 48G and 48GXs are what I mostly use. I also used to play quite a bit of Tetris on my first 48GX at university. The 28S is nice since it folds up, protecting the keys and display, thus making it one of the few truly pocket calculators there is. And while I was still doing some university teaching work, the 42S was fun to give to an unsuspecting student who needed to borrow a calculator briefly. And then there's the Droid48 emulator for Android, which beats the pants off any other pathetic calculator app. It's free, has no ads, and looks and works just like a 48GX. I've never tried to install Tetris on it, though it should be possible, I guess.
The furry cow is not an original HP accessory.