Is there any difference in sound between a Jerry Freeman Tweaked Generation Brass whistle vs. a Jerry Freeman Tweaked Nickel whistle in the same key? If so, what’s the difference? Also, is one louder than the other?
I have them in both materials in both D and Bb. The nickel one sounds shinier and the brass one sounds redder. 
No seriously, I can’t tell any difference between them. The brass ones are a little easier to hold on to for a beginner, because the nickel can be a little slippery, if that helps. I carry the nickel ones with me, alternating between D or Bb depending on my mood. Why, you may ask? I just like the way they look. I play them all. Pick the one you like. The differences are insignificant once you learn to play.
Buy them both. Jerry is a great guy and needs our support. Get a D in brass and a Bb in nickel. And don’t forget Jerry’s new A. It’s a great start down the path to low whistles.
Michael
I prefer feel of brass Gens. To me, nickel Gens feel slippery.
i love my freeman whistles, but did not like my Bb in nickel. too much chiff (airy) for me. the D and A’s i have in brass are not that way.
of course, that was the only nickel one i had, i didn’t have the luxury to try 10 or whatever, but that’s my experience.
brass does patina for that “played” look fairly fast, so if looks matter, keep that in mind. the nickel seems to scratch easier though.
Some say the Nickel feel slippery…this is correct but I like that because it makes them easy to play but I like the sound of the Brass(warm) more so than Nickel(bright) but I’m spliting hairs here. I buy both! I have not gotten a bad whistle from Jerry Freeman! I have them in D,G,F,Bb,A,C etc. Nickel and Brass. 
His latest Brass A whistle is really something. Have Fun, Mickey,
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Strategically placed pieces of matte Scotch Tape will kill the slipperiness of a nickel whistle.
OK - you guys are killing me!!! Are you serious? “Slipperiness of nickel whistles”? I can’t take it anymore…Arrrrgggghhhh…I mean does it like fall out from your fingers whilst playing? Do your fingers turn blue from grasping it so tightly? I apologize…a bad moment there. I have both the nickel and brass gens and they’re all fine; comes down to do you prefer red or blue plastic fipples…
Philo
I like red better than blue,
How about you?
To me, it does feel more likely to slip. It makes me think about holding rather than just playing. No blue fingers though, just more thinking 
The trick is to play those nickles until you wear off the plating under your thumb.
Nickel can feel slippery if your hands are dry. Just “huff” a little moisture onto your fingertips before you pick it up, or moisturize your hands before you play, and problem solved. Also, what Aanvil said.
Scotch tape on the fingers works for me too. Alternatively try rubbing your fingers in your hair before playing to generate static electricity, which will hold the whistle in place, although you might generate the odd spark.
If you have oily hair that would really slick up the ole whistle too.
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