I've had good experience with them, but it does depend on the dog. I live on a busy highway and coming when called is a must. It only took two "corrections" with my daughter's blue heeler and he comes every time I call now (that's with no collar). I have used them on several others with very good results. You MUST use it along with a training program though, and not as a punishing tool. Anything Tritronics brand is good. Get one that has a beeper also. Also get one that has adjustable settings. Many dogs only require the lowest setting.
I pop myself with it to get a "feel" for the settings. I can tell from your posts that you care about your dog! Good luck!