These are braces or splints that you are alleged to use during the night and they are believed by people who market these to fix the bunion (or more correctly termed ‘hallux valgus’). When you consider the photos of bunion correctors, it's easy to understand how they might do this. The question then will become, do bunion correctors actually help?
Thinking about the science along with biomechanics, you can actually see how the splint might make an effort to correct the position of the toe when asleep. The only problem with that consideration is that the following day you've got all of the pressures of weightbearing and also the shoes shoving the big toe back the other direction. It's probably likely those stresses readily defeat any kind of correction that can have taken place over night, at least theoretically.
Exactly what does the actual evidence show? One investigation has demonstrated that bunion correctors do basically help. They showed an improvement of a few degrees after a few months of use, which seems a great outcome. On the other hand, just what the research failed to show (and no additional investigation has looked at) is that if there is anymore improvement if it's used for longer or if the improvement is preserved if utilisation of the bunion corrector is stopped. Based on this it will be hard to give advice on if the bunion correctors will give you results at helping the angle of the big toe. That does not prevent a lot of people posting should they help in forums and Q & A groups on the web.
While acknowledging that, it does not necessarily show that they don't have there uses. Nonetheless, that use generally must be combined with the use of exercise movements in addition to footwear fitting guidance. Bunion correctors are often primarily effective at increasing the range of motion of the joint which may have a considerable impact on the ‘aches and pains’ coming from inside the joint which could be frequent in those with hallux valgus.