I have those exact same pads, even my marker writing with the grit looks the same!
I like their flexibility and the ability to have the un-gritted edge ride against a side piece and not scuff it, like when sanding a recessed box top panel.

I also have some of those "bricks". They are usually too coarse and stiff for my uses (and $$)
The pads last "ok", but load up quick so a blasting of compressed air cleans them up.