Rigidity is, for sure, the most important feature of a guidescope, with field of view probably second; optical quality—flat field, colour correction, and so on—isn't really important for guiding.
Also, don't forget: to guide correctly you don't need extreme focus or pinpoint stars—quite the opposite. A bit of defocus can actually help compensate for atmospheric turbulence (bad seeing).
The only drawback of the traditional, sturdy focuser is that it turns the camera while focusing, but that's not a big deal.
In the comparison video, both focusers are at their max travel, with the brake—introduced by Lunatico in this scope design—screw tightened.
When we find an improved design with both the rigidity of the older design and the convenience of the helical one, we'll update this post.
Jaime
PS: funny as it is, these new helical focusers aren't really a thing for optical astronomy either, since rotation of the eyepiece isn't a concern.
