I use the Cardiosport "Go" and can't complain about reliability. The "Go" is also a very entry level unit. It seems to be relatively accurate although I have yet to manually take my pulse and compare it to the unit. The chest strap and unit itself are well constructed.
It was an inexpensive gamble that paid off as far as quality goes. However, I do now regret not getting a device with a few more features. Specifically, I would have liked an out of zone alarm.