I have a Tourratech ( Kahedo) seat for mine , it is a vast improvement BUT as it is the tall option even with a 32 1/2 " inside leg it gets a bit tippy toes at times so usually use the standard and an Airhawk.
For anyone with say a 34" iside leg or longer it would be perfect.
That said the standard GSA seat is one of the best BMW seats I have used