My name is XXXXX XXXXX you for using JustAnswer.My name isXXXXX am an exercise physiologist and fitness expert here on Justanswer.comTo answer your question the importance of calcium absorption and utilization is dependent really essentially on the amount ingested but also on Vitamin D along with a stimulus to use and build (weight bearing etc). The reason you see a million different supplements is because of all the competition among supplement brands and the fact alot of companies try to prey on consumers. Vitamin D is important so its good to get that with a calcium supplement but assuming you are eating a healthy diet and not deficient in anything else, you really dont "need" a crazy marketed supplement.I will give you another example of how the supplement industry tries to prey on consumers. There was a huge time where a "1 hour window" following a workout was basically mass marketed to the bodybuilding and weight training community. People bought it, everyone was buying up all these "after workout specific" supplements. It really wasn't needed but the consumers bought it. Research now shows there is no magic "window" in bodybuilding so of course the whole tone has changed.In short, if you wanted to purchase the multi supplement(K, Boron etc..) thats good if it makes you feel better or if your diet is lacking some quality, but Caltrate and Citrcal are great products. I would use them without hesitation.The supplement industry is a multi million dollar marketing industry with some products that do absolutely nothing but are marketed as miracles. In short, in fitness and health there isnt magic only good nutrition and good healthy habits. Citracal and Caltrate will do great for you choose whichever one you like or is priced better per serving where you are buying.