Another here fighting with the 3rd hands...., It is also curious how expensive the 3D Holders they are, I understand that the Arms are High Quality, some of them Hydraulics but even so the price for them for dial indicators for example are not so expensive...
I took some ideas and make my own version, it require some tools, but maybe give some ideas...
Basically I did smaller bases to dont use the bulky magnetic bases they come with, also I changed the head for a part in which you can insert different tools, for example support for oscilloscope probe, or for Sensepeek heads could be used as well, since the tool is hold by a screw stud.
I like the idea of the bearing, I might check how it works because it is true that they tend to loosen when you move the arm end on the directions of loosening the thread.
I am still looking for good quality crocodile clamps...., not sure if they will be better than the ones from Aliexpress...
For the price of these arms I thin these kind of solutions are totally worth it.
Some pictures below