We have found these very useful.
They improve comfort when used in the dinettes as those seats are too deep and too upright to be comfortable. We also use them in opposing corners of the bed in our 17 to create comfortable reading areas with great outside visibility, or we place them side by side to watch media on our computer placed on a box between us. Cheaper and more versatile than the option discussed above. Also, that option has a lower cushion which will make the seat several inches too high to be comfortable.