I have run my dog for 4 years, 20 hunts a year (Texas coast) with the original Avery vest I bought her.
Make sure that the vest fits correctly, it does make a difference. The key is not that the area protected by the vest stays dry. The key is that the area under the vest gets wet, then the body warmth of the dog will warm the water and the water creates a barrier between the dog and the enviroment. This is the same principle of a divers' wet suit. If the weather conditions are too bad, keep an eye on your dog. The vest helps the dog stay warm, it is not a 100% solution to the problem.
Good luck.
WS