I too scratched my head on which set to get. They have so many different parts and the Festool site is a bit murky at first glance.
I saw a post by another member talking about the Vac Sys and it started me down that expensive road...
Just so happens I'm building a set of kitchen cabinets and the Vac Sys is saving me a bunch of time. And then I found the Sedge video and that demo put me over the fence on buying.
Anyway, I ended up getting the 203149. I wanted just the 203148 with a single clamp, but the only place I could find a Vac-Sys somewhat locally only had the 2 clamp setup. I was going to wait on the extra head, but it's nice to have it now instead of worrying about availability when I need it.
You get two of the clamping heads with the 203149 kit - including the oblong that comes with the head kit.
You will save about $40 if you but a complete kit vs buying the SE2 clamp later.
If you plan on bigger stuff like doors and taller bookcases then it's worth considering the 2 clamp kit.
Kinda rambling at this point, but it's one of those really helpful/unique Festool systems that doesn't get as much attention as something like the Domino.