I do not use a finger whistle. I attribute my choice to having started officiating basketball before football. I have pretty good whistle control.
(That is, last IW was a few years ago.)
I tried switching to the finger grip, as R or U as SoCA mentions, after a legal snap, but went back to the smitty 100%.
I just don't like not having to blow the whistle when I want to. I don't like the delay of bringing the whistle to my mouth. No change from 6 to 26 year olds.
As for giving half-signals, I think that is a characterisic of someone who can't as easily remember to incorporate proper mechanics.