Hmm, the thing with progress bars (as I know them) is that they only move right. A considerable slow down will stall them, without giving a hint about a new prognosis.

They often only show the amount of work done, like percentage of downloaded data.

But an ETA can adapt and give a better feedback, how long to wait.

Like if a torrent download is losing connection to seeders, and the ratio drops.

I still have to read this test in detail, I'm wondering by which objective criteria those algorithms are judged. (?)