Depends on the shirt. Depends on the length of you arms, and the strength of your triceps.
If it's a newer style high performance shirt (Rage X), expect it to take several months learning how to use the shirt for it to help at all.
An older style Blast shirt might give you 20lbs from the first day.
Try to find a Titan Fury cheap on Ebay. That way you'll learn how to use a modern style shirt, without spending a fortune.
You lift in Las Vegas?