Go on tell us who sent it as a freebie.I've just received one as a freebie, didn't know what it was until you posted that!
I suppose it might be useful as there's increasing use of barbless hooks that don't stick too well in the old lamb's wool patch. I solved that with a fold-over patch that holds the flies in, so it's stuck on the fridge at the moment.
I use one of the streamworks one as well. Stuck a strip of velcro on it and it sits, rock solid, on the fly patch on my vest. Had it for years and never lost a fly from it.Been using a Streamworks magnetic chest fly holder for years on my lanyard (was a link & pic on old site but search not finding it anymore)
Edit: search has found it see below, but some words not working! ( similar issue already reported to admin who are working on it)
Seem to be difficult to source now in UK, but it solves the issue of barbless, it has a reliable lid that prevent fly loss, slots to allow automatic drying out plus you can clip the lanyard through the slots!
Secure storage and convenient access to flies on your chest Unique, compact hinged box holds flies conveniently on the chest for quick fly replacement and drying. The stylish ergonomic design opens easily with one hand and forms a platform to quickly view and access flies. The closed holder...streamworks.com
As far as I'm aware and as Noeyedeer says, the Streamworks magnetic patch/box is (or was??) only available single sided. They also do a foam lined one but I can't think of a reason for getting that rather than the magnetic. Doesn't need to be double sided really as it will hold a load of flies. I once counted up after a few days fishing and there were 65 flies in it.is it the standard one you have or the double sided one