The Primos Power Crystal is one of the finer sounding crystal production calls.I have tried most all of the production models,and as far as glass or crystal goes it's the one.A good majority of the production slate calls don't rollover.They are almost impossible to get a consistant 2 note yelp out of.There are a few that will,but can't remember any of the manu.
I use custom calls,which can be expensive,but worth the cash.
Also if you have lots of swamps around where you hunt there will be woodducks,get a woodduck call and learn how to do a flying call,I get very good results using it in the am to locate roosted Toms.
Good Luck,
Mike