I installed my SR boost a few days ago. Yes, the plug is quite hard to get into place. I scraped up the top side of my wrist against the plastic trim trying to get it in there. It's difficult not only because of the tight space but because the orientation of where you need to put your hand means you're completely blocking your sight to the plug so you basically need sort of try and orient it correctly and then just go for it blindly. I pushed the passenger seat all the way back and slightly reclined and sat upside down in the footwell with my feet by the seat headrest. Probably took me about 15 or 20 minutes to get it. I'm sure I could do it much faster now that I have done it once though.
The speed boost is quite noticeable, it feels really good. If you always wanted your SR/SR+ to be faster and you have the 980 motor, I recommend it. I recorded some data from Scan My Tesla before and after:
Peak R power/R torque:
Before: ~228 / ~265
After: ~252 / ~307
Not sure how valid these numbers are, they were from just "regular" driving, not ideal isolated 0-60 runs but I tried to floor it at least a couple times during each data capture run in an attempt to get peak values.
I didn't really play with any of the other options (proximity door, rear heated seats, etc.) because they're not that interesting to me. I just turned on the ambient lights which are exceedingly mediocre. Such a dumb thing for Tesla to software lock to try and differentiate the trims.
Here's hoping I haven't screwed over future me with any kind of warranty issues/"flagging".