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Does anyone have experience with this practice mute? Is it worth the cash?

I use one and highly recommend it. Using it will open your throat allowing for more air flow and it help you identify your weak notes.
The person you really want to talk about these mutes is long time member here highams ( Charley Brighton ). He got me using it and can best explain the benefits of it. Send him a pm or email. He'll answer you.

From thw Wick website :
"Denis Wick practice mutes are perhaps the best teaching aid ever invented. Not only do they fulfil the need for the IN TUNE painless practice, so essential in the development of every young player and an indispensible 'hotel mute' for the professional, but they also possible an enormous improvement in tone quality using the entire vital capacity as a vibrating air column by opening the throat spaces through playing loudly in the low register."
In my opinion this is a understatement of what it can do for you.

Thank you so much for the input! PMing him now!