Happy birthday to me, a 'simply purple' cushion!
As with most products there are pros and cons. Different people probably would have a variety of opinions. Mine is as follows:
For a soft seat - such as a shaped car seat this only seemed to add pressure to the back of my legs. (Probably due to my excess weight.) However for a flat or solid surface I found this cushion is excellent.
This particular cushion is advertised on Purple.com and is the 'royal' model.