First off, I didn't found this project I'm not exactly sure how mandica came to the idea of doing it this way. I think that doing ring signatures via Tor is a good way to make an anonymous currency, and then again, the actual goal of this project is to have a decentralized system to exchange XSPEC to cash via mobile phones with other people. There needs to be some foundation for that, they could have chosen to base it on Monero or something different, but maybe they found that it's too complicated and too big for this purpose, so they based it on ShadowCash instead. Tor+Ring sigs are a very sleek solution that combines network privacy with transaction privacy. So it does the job well. You could maybe argue whether this is the "best" solution, I don't know. But I don't see anything wrong with it, either.