Foot orthoses or supports are designed to correct biomechanical problems of the feet and to improve the biomechanics of the foot. There are many different types of foot orthotics and methods of making them for doctors to use and choose from. A lot of people require and do benefit from customizable foot orthoses while some will be helped by the easier and cheaper mass-produced foot supports. Which one is right for each individual depends on precisely what is leading to the problems and just what the treating clinician suggests is right for that individual. All different foot orthotics include distinct design characteristics and a good podiatrist 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 symptoms.
Foot orthotics are not without their issues. If they are not the correct one for the individual, then they will not work. You are also restricted by what shoes you can use, in that you need to be able to fit them into the shoe and there may not be sufficient space. There are also types of shoes, just like the flip flops that they just can't be used in. This could pose a challenge in warmer climates that make closed in footwear needed for foot orthoses uncomfortable. You can find alternatives, for example, the Archies that have a foot support integrated. The shape of the arch supports in these Archies sandals are similar to what you would get in an over-the-counter arch support, but probably not as good as what you would get from a customized foot support. Using these do give a helpful alternative to foot orthoses, depending on where you can wear them and also the nature of the biomechanical issue. If you do require foot orthoses there is no harm in trying these types of alternatives or raising it with your treating doctor to see what they think.