Want to use it as a serious tool for self-development, long-term meditation support, etc.? Find a supplier that is in alignment with your own values and knows what they are doing. E.g. Holosync have decent entrainment technology, but make ridiculous claims and are very salesy and pushy... I have tried several and always come back to the Monroe Institute and their well tried and tested sessions, mainly from the gateway experience and lucid dreaming series.
If brainwave entrainment leaves you with unwanted side-effects (see below) or discomfort, you’re probably encouraging a range of brainwaves that are already excessive in some area of your brain. The way around this is to get a brain map to see what your brain’s strengths and weaknesses are, and see what (if any) brainwaves could use some encouragement.