Let's see:
Is it reliable?

It is based on your browser's activity: it depends, how often you request pages, and for how long you are logged in (60 minutes by default). You can spend days reading the forum as logged out, and only log in, when you want to post something. Also, you can write the whole content in any text editor, and just copy-paste it. Which means, that you can spend an hour on a forum, reading some posts, and writing some answers, but your "online time" can be just a few seconds or minutes, if you want to. And then, you can be active for years, and be online only for a few days at most.

Also, that's one of the reasons, why mailing lists didn't migrate to forums: because to post something, you have to be logged in. And some people don't like that: sending an e-mail does not require logging in, if you set it up in that way. Then, it is more similar to sending a transaction, where anyone can do that, without logging in anywhere.