I have a two sided horn whistle. One side is a peeper the other side has a pea.
I got mine from Cabela's.
If you can't find a dual sided one get a peeper type if you dog works close or one with a pea if the dog works out far.
It also depends on what you are using for the commands. I find it's harder to produce a double peep with the pea side.
But for me and a springer it works with the pea because a long blow is the come back so he's either lost or out too far. The short peep and double peep are for hupping (sitting) and turning so he's close and the peeper side works.
My dog works better with the whistle, especially while in the field. It seems to get through the will to hunt better than voice commands.
I suggest getting and carrying an extra of whatever you get.