Foot orthoses or supports are supposed to correct biomechanical problems of the feet and to help the biomechanics of the feet. There are lots of different kinds of foot orthoses and techniques of fabricating them for doctors to use and select from. Some people need and do gain from custom made foot orthotics while some can be helped by the easier and cheaper mass-produced foot supports. What type is best for each person will depend on precisely what is causing the problems and what the treating doctor recommends is the best for that individual. Many different foot orthotics have got distinct design features and a good doctor will attempt and match those up to the requirements of the individual. If that is not done properly, then there might not be any improvement in the symptoms.
Foot orthoses aren't without their issues. When they are not the correct one for the individual, they'll likely will not help. You are also limited by what shoes you can use, in that you need to be able to fit them into the shoe and there may not be enough space. There are also varieties of footwear, like the flip flops which they just can not be used in. This tends to cause an issue in hotter places which make closed in shoes required for foot orthotics uncomfortable. There are alternatives, as an example, the Archies that have a foot support integrated. The shape of the arch supports in these Archies flip-flops are similar to what you will get in an over-the-counter arch support, but most likely not as good as what you would get from a customized foot support. Using these do provide a practical replacement for foot orthoses, depending on where you can wear them and the character of the biomechanical problem. If you do need foot supports there is no harm in trying these types of alternatives or raising it with your treating clinician to see what they think.