Used Tritronics who first publicized escape avoidance training with the e-collar(now Garmin) for almost 40 years without a problem and Garmin is also a world leader in GPS. I consider everyone else a copy and although they may work OK I wont give in to a cheaper copy and have to buy twice.
I have the TEK 1, works well,battery life is a bit short for long days. Last year in North Dakota talked to another guy running one his had been in for repairs twice. Picked mine up on Ebay for 110$ no complaints for the price.