The Pooley's CRP-5 can be purchased with or without a wind arm.
I have one with a wind arm and find it useful since the surface of the wind side doesn't get discoloured and dirty with all the marks that have to be made on it.
However, they are used in a slightly different way so make sure you can find someone who knows how to use them in order to show you. I found that my study manuals only explained use of the flight computer without a wind arm.
Cheers
Whirls