I'm going to start this post by clearly stating that I am not a medical professional and recommend you speak to a doctor before taking any medication or supplement.
That being said, I love elderberry! I first heard about elderberry when the flu was going around and elderberry syrup and Oscillococcinum treatment was getting attention online. I then had a friend start talking about how much elderberry was helping with her allergies, and she isn't the type to jump in on fads. The next time I was at the store and Sambucol products were available I picked up some of the disolvable tablets to test out for myself. At the time I was dealing with a nasty bout of bronchitis, and didn't see much help from the elderberry. But when my son developed a cough, I gave him a tablet and the relief was immediate. He is only 4, so my husband and I try to give him as little medication as possible, but his cough was so bad we were trying anything we could think of to help him sleep a bit easier. We tried numerous over the counter cough medications and saw almost no effect. As soon as I gave him an elderberry tablet, the cough dropped to almost nonexistant.
Sambucol is the popular brand of elderberry products in my area, but there are others as well. They also have the product in gummy or syrup form. I take the gummies when my allergies act up (my son will not eat anything gummy), but I haven't tried the syrup at all.
Pros: Tasty! Seems to work (might be placebo effect).
Cons: Can be difficult to find due to popularity, might be hippy dippy nonsense
Overall: The stuff works well for me and my son, it might be because I want to believe it helps, but it really seems to. If you are looking for something to help with allergies and cold symptoms, you might want to try it out.