Could you fingerprint the browser to determine how many users are using the Tor Browser? Obviously this will miss the people who just use a normal browser through Tor. Or ask onion.to to log how many requests they are forwarding to you. Although, this will miss any other proxying service that happens to be running.
To clarify, TorSearch isn't accessible from clearnet (from my understanding) so he can't monitor->correlate individuals activity. Such as a nefarious search.
This is exactly true; however, if a user is coming in through the onion.to forwarder as provided in the article, remember that they can track anything that you do!
