Snow and ice will stick and freeze on the hair on the underside of dogs' feet. I trim that hair out, plus it just looks better anyway :) You can get dog boots, but I've not heard of a spray that will protect the feet from these elements. Good luck!
The Mushers formula looks good.
Please keep in mind that booties are annoying to dogs and also cover up their nails, which they need in order to grip on slippery ice.
I would never put booties on a labrador...