I have to go with the anti long board folks. I have not owned one in the 25 years I have done this work for a living. I had one just before I started when I was 17, loaned it out and never missed it. We all have different ways of getting things done.
I find that the 8" ND900 is THE most valuable tool for cutting filler. I have two, one as back up. If these tools went up to a thousand bucks today and I needed one, I would buy it, they are that valuable to me.
I have gotten pretty proficient using it and will do body lines and just about every size work. I rough out the work with it, then about 90% of the time will still "rub" a block over it just to knock any pokeys flat. I then skim coat it and switch to my 6" Dynabrade orbital finish sander (not a "DA" but an orbital) and will get it as flat as some of the guys I work with using a block!
I will go over that with a block 90% of the time to as flat as I can get it.
I say "I" but I have seen many guys do something similar. There are a couple of guys in the shop that do it exactly the same. One hardly ever touches anything with a block, 6" orbital only. I have to say, after the priming and painting his work looks the same as mine.
I do own an orbital long board that on particulary large panels I may pull out of the box. I use it VERY rarely, maybe twice a year.
Brian