FWIW I was always a bit unsure about the effectiveness of the TBM, until I cheaped out one day and used just the one bucket on my old car immediately prior to sale as someone was coming to look at it unannounced. The wrap went from still flawless to noticeable swirls in one sitting: I was gutted, and although no one normal would probably notice the difference, once you’re into making your car look good it stuck out like a sore thumb.
Always, always, always TBM. It really does make a huge difference!
Although I get that your back is stuffed and it’s awkward to do, if you can you’ll notice the difference. If you really can’t, then you need to be looking at getting a proper coating on there imho as at least that’ll be a bit harder to mark up, plus washing time is MASSIVELY reduced so the TBM takes a fraction of the time (like half, in my experience).