They are plastic, cheap and simple. For being so cheap they are quite nice though! Printing quality is good as well, well worth it.
Cheap to make Good for promotions
None that I can think of.

I ordered a button with my own drawing, the product came looking great. There were no issues with the image quality. A note however, I had previously seen the recommendation to make your image lighter as the printed result is darker. (my drawing was of a dark-skinned character) This is true as I made this image lighter just in case and it came out printed close to the color I had wanted! Definitely happy with the product!
Image looks great, no defects, came out just as I wanted.
None!

I've done a few for my fencing club so the kids may attach them to their sports bag.
Everything is perfect with this item. Nothing bad to say.
I haven't find anything bad about it.

I made this one to my son. For his backback in school. It turned out amazing. Great quality. Bright and stunning colours and a layer on the piture/printing, so I'm not so afraid that the rain will ruin it.
Everything. Really a good product here from www.kaz.website.
No

The badges are perfect, service excellent and no request to hard to fulfill...thanks ArtCow
Endless
None