That’s a totally reasonable question. The biggest reason is that Tor is just not making any kind of cryptographic guarantee of your privacy; it’s just kind of ‘statistically mixing’ your behavior with others.

The privacy guarantee we provide is categorically stronger. It’s a cryptographic guarantee, like the one that underlies ECDSA signatures or SNARKS. Tor is more analogous to going to a library and using their WiFi to make queries, whereas Spiral truly cannot learn your queries. You could of course always use both, if you’d like.

As you point out, in both cases, you need to run code on your machine. We hope that, over time, we get lots of eyeballs on our client code, and in fact, it would be cool to get it integrated into Brave, Tor, or as an extension for Chrome or Firefox.