Not sure how new it is. I know it's been out for a little while now. If your going to be hunting in rattlesnake country then I think it is absolutely a good idea. From the little that i have read it neutralizes the venom immediately, reducing swelling etc...
You might also want to look into snake break training if you are going to be spending time in rattler country as this will teach the dogs to avoid them altogether. Other than the dog just running into one and getting bitten from incidental contact, the training and vaccine are a good two step approach to protect your dogs.