Emits a lot of 'progress' signals

At the moment we are sending the progress signal every time the buffer from the reply is written to disk, so atm, it is intentional but I can certainly add some euristic.. maybe just send the progress after x bytes or x % (we cannot do a single value since we want to send progress for small files).

What do you think would be the best approach regarding the transfer indicator?

As part of the specification of the toolkit progress indicators, I've suggested that any change to a progress bar's value should be animated over 500 ms. If so, updating the value more than twice a second would barely be noticable.

Instead, or in addition, an app might display precise download progress as numbers. But except for highly predictable sequences (like a stopwatch), it's generally poor practice to change text like that more than about twice a second, because it's too difficult to read.

If both of those are correct, then there would be no need for the download service to send more than two progress signals per second.