Very interesting. Honestly, I have a Diana clone, and it takes photos that are at least that sharp, and sharper at close to mid distances. The lenses on these cameras are different from one camera to another, cheap, plastic quality variations being what they are. My other Diana F lens is not nearly as sharp, and I have checked the infinity and other distance focuses on both cameras w/a tripod and ground glass on the film plane (as much as I could w/ that tiny aperture). Here's a look at the lens you're interested in and how it mounts on the camera. No info on how to get the old lens off though! You're on your own there it looks like.
https://www.youtube.com/watch?v=ZaeDIwSvbbQ
The problem with buying what appears to be an improved 3 element design lens is that it will not have the same wacky imaging characteristics of the original single element lens. You're not going to get those neat distortions and aberrations, which is the appeal of these toy cameras. In other words, your photos are going to look like a "normal" camera took them, except for the soft corners. For the same amount of money you could buy a much better built Agfa Isola w/ a better shutter and a sharp 3 element lens that will take photos that rival any good medium format camera, and still be small and light, w/ a much better build quality. I love mine, it makes beautiful photos, but I prefer the shots from my single element Diana clone camera for their unique look.