If you can get the ROHO seat, I highly recommend it. Unless cigarettes or knives (or scissors) punch a hole in it, making it go flat somewhere the patch kit won't work, it is a great seat. I started out with a different one that came with my chair--later was given the ROHO and wish I'd known to insist on that from the get-go.
Seven inches rise sounds about right. I haven't measured (and can't do it myself anyway), but it does make a huge difference... being higher means reaching the faucet longer, being able to get into the top of the freezer, actually wash my face pulled under the sink (arms flip up). It means a great deal, apart from the transfers Kelly spoke of--which are really important.