I agree Doodledog - I can't see how they are different to a USB drive although it says they remove duplicates. However, this could be dangerous if you have photos called Image 1 and Image 2 etc. which may be different from ones from an earlier date with the same name but it will think they're the same photo? Cameras and phones all have their own way of naming the photos although usually this is by date and time nowadays which is good.
Some of these photo sticks are only 4Gb or 8Gb which won't hold a big photo collection. A lot depends on how large they are in file size. Older photos are not so large and I also have hundreds of scanned photos which are only about 800Kb each which is less than 1Mb. Phones today can take rather large sized photos which will use up a lot of space (3.5Mb or more).
For anyone who doesn't know about file sizes this is how they're measured:
Kb = kilobyte (small)
Mb = megabyte (medium)
Gb = gigabyte (large)