There is a lot of info out there about HR training and it does often conflict. First if you are going to striclty follow a HR Training plan then it can deifntley be beneficial to you and your race plan/times. If you are not going to take the time to understand HR training and follow a plan its probably not woth it even though there are some relaively inexepnsive HR monitors on the market.
Follwoing an HR Training plan not only helps you understand at what level your body can work but how to effectively train and minimize injury while increasing endurance and speed. HR monitors generally operate by sending a signal, analog or digital, to your watch from your chest strap. There can defintlely be problems with your watch receiving the signal but from my experience it is not Brand specific. HR straps and batteries can go bad and have a shelf life so you may have to replace them every so often. People generally just blame it on the Brand or model but the big brands use similar technolgy.
As in all sport watch technolgoy the more functions and features the more expensive the watch gets. If your not a triathlete or training for marathon PR's the base levels work really well. My favorite has always been the Timex Ironman Road Trainer (119.95) which also has and easy push Laps/Splits button. Timex Road Trainer gives you the ability to set HR zones and alarms to let you know when you move out of the zones so it essential works well with a HR training plan. The Road Trainer aslo lets you review alldata by laps with the heart rate at that poit in time so it has enough features but not too much. Polar and Garmin have decent HR monitors but for beginners they are too expensive for what you will need. If you dotn want laps/splits you can find HRM's for $50-$75 as well but then its strictly just current HR.