Using CaMg throughout the whole life cycle is a good way to cover your bases so you don't have to worry about getting a deficiency. I couldn't tell you the last time that I have ran into either deficiency since implementing it into my feedings. I also have not had any over feeding issue based on using it either, granted I'm using a form without any nitrogen content.
jbone I think you are right in what your saying in that plants usually don't have both deficiencies at the same time, however your message is being lost with an antagonistic form of dialog. You tried to "test" me when it came to the pk boosters question, and how over use of P can lead to issues, but if you know you are supplementing with CaMg already, in those situations it's easy to realize that you are not deficient in Ca or Mg(since your giving more to your plant on top of your base). I think your biased opinion of bottled CaMg is allowing you to shut out how it can be useful in ones garden, and if your happy using calcium nitrate and mag sulfate as a preventative measure or in treatment situations awesome. There is no need however to get so riled up over another gardeners use of a product that works for them and that may have solved their issues in the past.