I bought mine from Swansons online. Relatively inexpensive (8oz for about $9). I like using it to relieve muscle tension and headaches. DH uses it when he has a leg cramp. It isn't really an "oil" per se but mag cl and water. Absorbs into your skin. Some people like it while others don't
The only thing I can say about the electrolyte balance is to try a little and see how you feel. I like the idea of not having to ingest just one more thing and go the trans-dermal route!