I have them on my flatbow because
(a) they look cool
(b) I love the way they make the bow virtually silent, completely different to my
recurve
(c) they look cool
I haven't chronoed the bow with and without but to be honest my gut feeling is they are not slowing the arrow down by a huge amount as they are quite close to the end serving, it's a dacron string and as I'm shooting 32" long wood arrows with 11/32 shafts and 100gn points they aren't going hugely fast to start with.
It's at the heart of the reason why I also have a trad style bow with wood arrows as well as my
recurve with ACEs, and use a glove and leather bracer with the flatbow rather than the platform tab etc for my recurve. For fun and an antidote to the high tech.
Did I mention they look cool too?