I can assure you that they are good. But just like the difference between a good meal and a great meal, the ingredients and their source must be considered. Huh? You can take supplements and vitamins haphazardly but it does not make good sense.
Are you concerned about a specific condition or body system or do you just want to "stay healthy." Does something hurt? Did a commercial get your attention? In other words, why are you considering vitamins and supplements?
You would serve yourself very well by investing in a quality reference book on the subject. There are many of them available - and do not foget the Internet! I have many publications that I reference for writing these pages. My "elephant gun" is the PDR for Herbal Medicines. This is like the prescription manual for herbals. As a matter of fact, PDR stands for Physcian's Desk Reference. Now, thanks to capitalism, we can buy them for personal use.
You get a description of the item, how it works, usage, precautions and adverse reactions, and dosage information based on what form it is in. Form meaning powder, pressed pill, capsule, liquid or other form. The thing I like best is the literature listing that was used for the information. Knowing who did the research and what kind of research was done is important.
Taking supplements without direction makes as much sense as asking a doctor for a prescription for a medication for which you do not have the condition or disease. Being proactive in your health care situation is prudent, be armed with science based knowledge and be healthy.