Not for me personally, others might like such a thing.
I sill have my GM1 camera bodies that have no evf and can be used with small lenses for less serious stills work but I have fitted them up with VEfinder stub mounts to which my device clicks on in an instant. Then I just frame focus through the VEfinder lens and the lcd effectively acts like a large evf. The stance and grip mimics the traditional grip: eye to evf/VEf, left hand under lens to grip and right hand works the body grip and shutter button.
My idea was with a S9 as I already have all the camera body stock that I could possibly need in M4/3 mount. If I want horsepower: G9 or G9II. If I want light and fairly compact: the G100 or GM5
My idea was with L-Mount where I only have the rather large S1 (I am happy with it). I would use a S9 as an experiment and fit a VEfinder stub mount to it so that I could use the lcd as a form of evf like I have happily done with the GM1, Pentax Q, and Ricoh GXR - all camera bodies basically sold without an evf that can be used easily with an open loupe to get the added benefit of an easy-convertion to much of the benefits of a camera body that had an evf.
The GXR type did have a clip-on evf but I found that it seemed always to have been left back at base whilst my VEfinder, when folded, fitted easily in a corner of a bag or simply in a pocket.
Here it is yet again - simple and sweet*
https://www.dpreview.com/forums/post/59525486
* those that like great big clear evf units will not be impressed, but for those that just need a handy device to convert their lcd into a usable evf for framing and focus checking could find this handy. I only made this for my own pleasure after about 14 prototypes.
There is/was a similar commercially made device called a Clearviewer.
These devices focus your eye on the light being emitted from the lcd and disregard the external ambient light. It is quite remarkable how it works. Those that complain about not being able to see the lcd in bright sunlight tend to blame it on glare. But it is not the glare that is to blame it is that the ambient bright sunlight that shrinks our pupil and the light emitted from the lcd is not strong enough to compete. The loupe works even if it is an open type as your pupil will now get most of its eeen light off the lcd alone. There is also some glare that only a close loupe can eliminate but glare is not as big a deal as popular legend portrays it.
The open loupe is quite compact and can be folded when not in use. The closed loupe is huge.
My VEfinder was an invention of necessity 10 years ago but has gone into recess since my new gear has always had usable evf units since.
