Thanks for all the info on the S models, you answered all the questions Gitzo's site couldn't!
I use an Acratech Ultimate Ballhead, and it looks like the quick release knob might hit the tripod when pointing down and attached without a center column, but this shouldn't be a problem: in the hypothetical case where I would want to point the camera directly up or down I could just flip it in the QR clamp so the knob points up.
I was surprised that the low height of GT3531S, thanks for pointing it out. The heights are not listed for some unimaginable reason on Gitzo's product description page. It looks like I might need to go all the way to GT5531S to get face-level height with my smaller cameras. I'm afraid to check out how much
that costs. I'd be using it mostly with TLRs so most of the time the low height is an asset, but sometimes I want/need to go higher, and without the center column it wouldn't be an option. Or I could get the optional center column for the GT3531S. Decisions.
Gitzo really needs to get their website in order. And can anyone get their
tripod configurator to work?