You can now play this game for free on Itchio:
https://sylvie.itch.io/you-are-such-a-soft-and-round-kitten
Or on my website:
http://love-game.net/10mgPresentsYouAreSuchASoftAndRoundKittenBySylvie/
There are no significant differences between the downloadable version and the web version. The reason the downloadable version is not free is because:
1. To make a Steam game free, I have to manually contact Steam Support and ask them to make it free.
2. The game is part of the 10mg Bundle and I don't know how making it free would affect the bundle.
I do not recommend purchasing the downloadable version unless you want to support me by giving me money, or if you really want this game to appear in your Steam library.