I'm not at all impressed with the quality of the Fly Roost device; it's very rough poorly printed plastic and the magnet tends to fall out.
While this (and many other devices designed to facilitate threading tippet THROUGH the eye of the flyhook) do indeed accomplish that part of knotting on a fly none of them actually help threading the tippet through the small space between the tippet winds and the outside FRONT of hook eye....which is every bit as challenging as the original problem solved by these threaders.
I am not visually impaired nor dealing with any sort of tremors (yet anyway) but I have acquaintances who have such problems and have tried out several of these aids in an attempt to help them keep fishing, but so far haven't found anything that eases their frustration.
At some point the frustration (including frustration of having to rely upon fishing buddies who are quite happy to assist in those tasks) begins to far outweigh everything else.
It's sad to watch somebody lose access to an activity that once provided so much personal pleasure. Unfortunately visual acuity and steadiness are key requirements for both flyfishing and flytying.
If you find one that gets it through the eye consider changing knots. Something like the uni can be tied with a big loop and a long tag. Will cost you a lil more in tippet......but I think the ease is worth it!
I'm 53 and keep on of those orvis flip down magnifiers in my bag. My buddies pick on me when I use it......then they ask to borrow it!