Working from home I have a fairly comfortable but thinnly padded chair that feels a tad uncomfortable after an hour or so (a shame MightyApe doesn't have facility to include photos in their reviews).
This cushion makes a huge difference in comfort for me, so much so that I bought a second as a spare for the day (hopefully in the far future) when this one eventually need replacing.
Absolutely worthwhile. Quite a decent size (about 60cm wide by 35 deep) and mesh cover allows airflow.