This is the best product for those times when you have broken something plastic and there are missing pieces when you try and put it back together. This is a plastic welder. It uses the same technology as what your dentist uses to fill your teeth.
I have used this to successfully repair keyfobs, cellphone cases, car body parts, cable casings, etc.
It works best when the parts are clean and it can fill in the missing gaps so I always prep the parts to allow for a slight gap then "gluing" parts together. The most successful repairs are done in layers rather than all at once. Cure each layer as you go. it only takes about 4-6 seconds exposure to tge UV light to permanently cure a layer. I have also found that sometimes using some form of reinforcement (like a thin wire frame) allows for the fabrication of larger gaps in missing materials. Afterward it can be sanded to finish the fit.