I use it often with Yin Yin. It is perfectly safe - not so much herbal as homepathic. The cheapest place to buy it is SuperStore - Provigo in Quebec or Loblaws in Ont (all same company). You can pay extra few dollars and get the identical product at a health food store.
I also like cocculine which a vet told me about - helps animals sleep while travelling and since it is not an anti anxiety drug like valium, will not affect the pet's metabolismnor make them groggy.
I'd go with Rescue Remedy first tho.