I would never pay for or want to lug around a grace space bar. seems like overkill.
Ahhh - but I can accurately set up an ORTF pair of cardioids in less than 30 seconds as distances and angles are all accurately marked.
As a Spacebar owner, this is a pretty far stretch from my user experience. The distance markings are only relative and you still need a tape measure to determine exact spacing between the capsule diaphragms or you will need to have a chart, specific to the shockmounts and microphones being used, to accurately space the microphones. In addition to that annoyance, the angle markers are accurate, but it is very difficult to keep the shockmounts perfectly aligned with the 0 degree marker because the black spacer (or I guess it's really a stopper) easily turns. In the field, this means setup time is more like 5-10 minutes and NOT 30 seconds, but YMMV and perhaps your fingers are less klutzy than myself.
The Spacebar excels when it comes to needing to reproduce an exact configuration, but setup time is not quick by any means, especially if you use more than one type of shockmount or microphone and for what we do the K&M is usually better.
What you say is correct for the first time use - but once you have done it once you will know the bar measurement for that mic.
For instance I know that with my MKH 8040s in Rycote InVision mounts, the bar measurement is 3.5 each side to give me the correct 17cm capsule spacing.
All you have to do is to note the bar spacing the first time and you can set up exremely fast the second and further times.
My 30-second quote was based on the second time I did it, not the first.
All you need to do is to note the bar distance the first time you use a new mic. and it's quick and easy after that.
I always find the angle very difficult with an unmarked bar, more so than the distance measurement - the SpaceBar makes it very easy.
That's my personal experience, using it in anger.