If you can find a mouth reed that works for you, I think you have more flexibilty in the sound you are making and you can almost play it like an instrument to make the sound you want. You can make decent sounds with the built in versions but again you need to find the right one that works best for you, unfortunately they are spendy to find the right ones. The main thing is to practice a bunch the first year you get into it, then after that it is easy. The time spent is worth it, my best hunting experiences all revolve around having called a screaming elk to within 20 yds and have him raking a tree and chuckling right in front of you....AWESOME!! Good Luck!
Mike