The 0 refers to which Google Apps/Gmail user session you want to open. For example, 0 gives me my personal Google account, 1 gives me my work account.

I guess h stands for html.

I find this interface to be slower/all-round worse than the JavaScript one. Maybe it's because I don't live in the US and notice the 500-700ms+ page render times more when the whole page reloads.

Thanks!