We had it done a few weeks ago, just before we went on a 1600 mile trip sharing driving. We're pleased with the modification. Our complaints differed, but were both based on the seat bottom being too hard. My wife found it painful and I didn't like the lack of lateral support (I slid from side-to-side on turns). After they modified our driver's seat, sinking lower solved my lateral support complaint and the softness solved her complaint.
I've always set the seat position all the way down. Although it wasn't a complaint of mine, I also now like the slightly lower seating position better (I'm 6' 1").
Initially, I thought it odd they only modified the driver's seat and not the passenger's, but after our road trip neither of us were uncomfortable in the passenger's seat even though it's noticeably harder. The only reason I can imagine for the differenence in comfort is that as a passenger you unconsciously are able to shift your position often without being "locked" to the pedals and steering wheel.
BTW - The seats we're accustomed to are our Mercedes S550 and SL500 seats, which are still slightly better overall than Tesla's seats.