Although I have heard of it, I have never used "Dave's Flexament", so I don't know whether it works in the same way! There are a lot of glues and stuff which DONT work for this, or cause various problems.
The UHU is a gel type glue which does not string or run, it dries perfectly clear and flexible in seconds ( when used on feathers like this).
I am always a bit wary of things I don't know anything about!
TL
MC