I am not a scratch builder. So my use and knowledge of disc sanders is limited. But I will add a point for you to take into account in your selection. Something that I found bothers me a lot.
It is the case around the disc:
All the following have the disc within a body case. If you want to sand a piece of wood that have an angle, let say like an L, you will find that metallic case will stop you to sand all the interior of the L.
I hope you understand what I am trying g to explain.
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Do you see the case ?
The Byrnes do not have that case.
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But the constant speed is strong. If you do not have a steady hand, oversanding can happen.
I have the small proxxon, due to the case I decided to buy the Byrnes too. But due to the speed I received recently the Ultimatium Sander. No case and hand speed. Below I pasted Olha's video.
With the 3, depending on the task, I use one or another.
Cheers
Daniel