For cameras with a grip like the Sony a7 II series of cameras, this makes a lot of sense. But for cameras like the Olympus Pen F, the Panasonic GX7 and the Fujifilm X Pro 2 with a rangefinder style body the use of the SpiderLight may be more cumbersome. The reasoning behind that statement has more to do with the fact that those cameras require you to put more thumb pushing pressure than all four fingers gripping pressure.
Straps like these have been made before, mind you. The Peak Design Clutch wrist strap does pretty much the same thing. Their Kickstarter video is after the jump.