Had my car (which has the new non-adjustable headrests) go in for service at tesla and was provided a loaner 2018 100D with the older seats with the adjustable headrests. The first thing I noticed when I entered the car was the seats being less comfortable, I immediately missed the newer seats. They seem quite a bit narrower and generally provide less support (at least for my body type). I also noticed the adjustable headrests are quite a bit firmer than the newer seats which feel like pillows in comparison. While I thought I would miss the old seats configurability, after this experience, I won't be looking back at all. I thought I would share and see if others noticed this difference.