I had a sportdog 1825. I had problems with it since day 1. Noticed early on that often when you attempted to apply a "nick" the dog would not respond. Then you would attempt it again and the dog would respond. For a while I thought I just did not have the intensity at the right level for my dog. Same thing would happen when I turned the intensity up. Dog would not respond at all and then the next time he would yelp because intensity was obviously too high. Then I decided to strap the thing on me and walk 50 yards away from my buddy. Sure enough when he would attempt to Nick me it would only go through maybe half the time. Sent the collar back and they sent me a brand new one. IT had the exact same problem. GO with TRitronics. Sport Dog is very inconsistent to say the least.
I really liked the 1825's features, but I was having the same problem with inconsistent corrections. I just ordered the Einstein collar yesterday.