[Custard: the epitome of common sense, as always! Below was written a bit earlier today, but not posted.]
Surely it's not the case that one of the two block designs is absolutely better than the other?
I put a lot of softwood through my little Kity "hobbyist" machine, and for that it's pretty good (although a bit slow and under-powered). It struggles with hardwood, even with newly-sharpened knives.
But I was up at one of Peter Sefton's open days a few years ago, where he had organised a demo of the (then new to the UK) Hammer spiral block, which was very impressive, particularly on difficult woods. The finish was almost what you'd get from hand tools.
The spiral cutters slice, like a skewed plane iron, whereas conventional cutters don't. I see the same on my rebate cutter on the router table - the carbide is skewed - you really do see the difference, in a cleaner finish with less (usually no) tearout.
Then there's the thing about knicking a knife on a nail or a bit of grit - you don't lose a lot of material from the knife on a regrind, it's just a matter of finding the damaged cutter and either rotating or swapping it. It suggests that the cost of ownership should be better, but I'd be very interested to know if that's true or just wishful thinking.
Given the time it takes to properly clean my own PT after running softwood though it, I can see that a spiral block might gum up more and be a nuisance in that context, so it's reasonable that standard knives would be better.
On noise, I was surprised that the block was noticeably quieter than Peter's standard planer (of similar size; the Hammer demo machine was next to it), but not so quiet as to go "wow!".
To enlarge a bit on MikeJhn's comments, for a meaningful comparison it all gets a bit technical: you have to consider the noise
envelope: not just how loud it is overall, but the nature of the sound. High pitched sound can be absorbed relatively easily, and doesn't travel very well. Low sound is much harder to deal with, but also less of a nuisance, because most machines don't emit a lot of it (relatively speaking).
I would expect, based on experience, that a spiral block
actually is much quieter for a number of technical reasons, because the percussive, impact noise will be a lot less, and higher pitch. BUT... whether that is a significant part of the overall noise of the machine, is another matter altogether.
I was going to talk here about how difficult it is to measure noise meaningfully. I've moved it into
a fresh thread in General Chat, if anyone is interested. If you're bored by that sort of thing, just don't read it (nobody is forcing you to!).
Happy New Year, all,
E.