The On is way more expensive now because they stopped making it a few years ago. The Uni is newer so it's easier to find and cheaper. I don't have an Uni but it seems more similar to the Pix which I didn't like very much, I prefer the On because of the gene mixing and being able to have a unique tama (and name your tamas) instead of raising the same ones over and over, and your tama doesn't die easily (not sure about Uni but my Pix tamas die all the time)
Also the main reason I don't want an Uni is that there's apparently no way to turn it off or pause it if you want to take a break from it (people say things about letting the battery run out but some people have reported that it doesn't work and their tama dies)
