I couldn't disagree more. I have used Transdermal Magnesium Oil (TMO) for a number of years now and have recommended it to many people for issues ranging from diabetes, chronic fatigue, heart disease and osteoporosis. Magnesium is bulky so they put very little of it in multivitamins. Magnesium supplements are either poorly absorbed or require multiple pills daily to increase levels. Only 1% of magnesium is in the bloodstream. Measuring the RBC levels is a better indicator of adequate levels.
People who are ill are generally on multiple medications or supplements. They dread even one more pill. They find it easy to use the transdermal oil. It is a wonderful method of delivery that takes into account patient compliance. (There is no sense in recommending something people will not take).
Here is a lengthy discussion on it, including documentation of increased red blood cell levels after usage. Dr. Mark Sircus has numerous references to research and diseases helped by TMO on his IMVA website as well.