I didn't answer your poll since I have not flown my 8 yet but.........
Most A/C have at least a trim tab on one ail., so if you don't mind dinking with that, are alright with its limited capability and utter lack of easy adjustment; leave out adj. trim.
I have just started flying my -8 and have found that after a bit of flying, something starts itching in my head...oh yeah...I forgot to trim her out. A quick nudge on the trim tensioner and the itch goes away.
It is very subtle, and you would do fine without it, but it sure is nice to adjust to hands-free. For something that takes only a couple of hours and a few Avbucks to install, I say it is worth it.
Initially I installed the manual cable in my 8A. I didn't care for how it worked and put in the servo during phase 1. That said I only use it when hand flying in very smooth air to offset any fuel inbalance. I switch tanks every half hour so an ocasional flick of the hat switch is all that's ever needed.
We fitted the (Manual) Ailn trim, but didn't like it's interference with the controls - both the springs, and the notchy interaction. I am sure with effort the latter could have been remedied. Hence in final build we just left it all out... and have never missed it
I have flown ~5 other RV-8s, and in one I would wish for it - it exhibits a heavy L wing at high speed, and R at slow. All the others had the "heavy wing" across the speed range, and cured by the usual means.
However, little of our flying is long distance cruising...