I'd vote "cosine" units on the device --

You can use software or prepare you charts to handle the cosine value with little to no extra effort...

HOWEVER, if you ever find yourself without your Pocket PC/charts/calculator and have to do the math "by hand" in the field, simply multiplying by the cosine value supplied by your angle measuring device is a helluva lot easier than multiplying by the square root of (1 - sinē X), where X is the angle in degrees read from your device

At least for me anyway...

I guess you could commit cosine tables to memory -- but who has braincells for that?