Foot orthotics or supports are designed to correct biomechanical problems of the feet and to help the biomechanics of the feet. There are several different kinds of foot orthoses and techniques of fabricating them for podiatrists to use and choose from. A lot of people need and do benefit from custom made foot orthoses while some might be helped by the simpler and cheaper mass-produced foot supports. Which one is best for each individual will depend on what exactly is causing the problems and just what the treating podiatrist suggests is the best for that person. All different foot orthoses have different design features and a good clinician will try and match those up to the needs of the individual. If this is not done correctly, then there might not be any improvement in the issue.
Foot orthotics aren't without their problems. When they are not the correct one for the individual, chances are they will not help. You are also constrained by what shoes you can use, in that you have to be able to fit them into the footwear and there may not be adequate space. There are also kinds of footwear, for example the flip flops which they just can not be used in. This tends to cause an issue in hotter places which make closed in footwear necessary for foot orthotics uncomfortable. You can find alternatives, as an example, the Archies that have a foot support built in. The design of the arch supports in these flip-flops resemble what you should 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 alternative to foot orthotics, depending on where one can wear them and also the nature of the biomechanical problem. If you do need to have foot supports there isn't any harm in trying these kinds of options or raising it with your treating doctor to determine what they think.