I use a shock collar as of the last couple months because Chance, who is 3.5 and been 110% reliable off leash with an awesome recall since he was 6 months old...Randomly decided he wanted to run up to any person he saw, ESPECIALLY if they had a fun new friend to play with!!!!
I really regret not getting a rechargeable one. Though I did find a "nice" offer where for $26 a year you get a new pair (2) batteries mailed to you (free shipping) every month. (About as long as a pair last when kept on for several hours a day) So it averages out to a little over $2 a month for a set of batteries, MUCH cheaper than the $7 ones they have at Petsmart!!! O_O
I do love the collar though (Sportdog brand), it only has 8 levels but Chance works on a 2-3. I've tried all the settings on myself (And discovered a spot on my hand where if I put it and keep pushing the button the vibrations make my thumb move! LOL!!) and NONE of them are painful. #8 is a little "shocking" (no pun intended) but it doesn't -hurt-. Which makes me feel a lot better since I don't want to -hurt- him, I just need an extra hand in saying "Hey, don't forget I'm here and you have to listen".
I will say, if you are looking at an e-collar to train your dog, forget it. Everything must be manually trained and understood what is being asked of your dog before you can even think of bringing in the collar. If you ask the dog to come to you and the dog doesn't know what "come" (Or whatever word you use to get your dog back to you) means, you can't shock him for not doing what you ask. That's unfair and VERY cruel. Chance has been trained with NILIF since day 1 and again, it wasn't until 3 years of positive treat training that I brought in a collar. It is used for a reminder, NOT training. Shocking the **** out of your dog will do nothing but confuse and scare it.