For my cnc router that has an ER20 spindle taper, I got tired of the tool length changes etc. So I made a series of solid holders that were ER20 and then either a standard tool size like 8mm 6.35 for 1/4 inch, 6mm and 4mm. These were bored at the time the holders were made from the bar.
I also made a series of ER20 solid holders that have an ER11 taper and thread on them. The ER11 holders, have a thread in the back for length stop adjustment, so that the cutters etc can be the same length.
So the tools can be changed and not have to scan and reset every time. They are very handy to have on the mill when wanting to change out a cutter to another size. The collet nut, does not need to be any where near as tight compared to holing the cutter in the collet. But not as quick as changing in 10 seconds though. But is quicker than changing with a loose cutter and a collet.
There are companies like Big in Japan that make nose fitting tooling for high precision milling.
I am sure that there will be a way of making something up to get repeatable tooling lengths, but the Cutwell System is very slick , and the 3k rpm limit is ample for manual machines. I am sure that you could play with the installation to get the best possible run out with your machine.
I would want to get quite a few of the different holders for sure, and like you mentioned, that becomes real money very quickly when the main adapter, and then the various holders. I am sure that you could make your own holders, but won't do it for the price they are selling them for.
Removing the tooling from the spindle every now and then is a good thing, as you don't want frozen or jammed tooling in the spindle.