Bunion correctors are splints or braces that you wear on the foot at night with the aim to correct a bunion. They work by holding the big toe in less of a valgus position to try and straighten it so that the bunion is not as bad as what it was before and the associated hallux valgus is improved. They can only be worn at night as there is not going to be the room to fit them into the shoes and they are not exactly made for walking. There are other less effective devices that you can wear in the shoes during the day and are a good option to help maintain that night time improvement.
The bunion correctors can take a long time to work as you are talking about changing the alignment of bones which is going to take a while. The other problem is that you put the foot back into footwear that might put pressure on the toe back in the other direction during the day time when you are not wearing it. Kids who wear braces or retainers on their teeth to change the alignment of the teeth need to wear them for a very long time to get an affect and kids bones are more likely to be remolded. In adults trying to remold the bones of the foot is going to be a lot harder and take a lot longer. This means that bunion correctors are going to be a long term intervention and quick results to correct the bunion are not likely to happen.