If the dog has been trained properly, they will respond no matter if the collar is on or off. All my dogs obey the same regardless of whether or not they are wearing their collars. Properly trained, they learn to be voice conscious not collar conscious.
As far as price, I am a firm believer that you get what you pay for.
SitMeansSit is a great technique to dog training I own a dog training company and have been training dogs for over 10 years now Tim Smith taught me the method of using an e-collar in a positive encouraging manner. I now use the e-collar on about 90% of my clients dogs. Sit Means Sit is a franchise but all of them must attend the school and graduate to become a franchisee. So the question is not whether they are capable of training dogs it is if they are truly dedicated to training dogs! Anyone can learn to train dogs but if it is not a passion they will never be good no matter what technique or school they went to! Check out my site at http://www.prodogtraining.biz for more info on dog training.