I own a Fitbit Charge also and wanted a second band so one could be for outside gardening work(i.e. Dirty) and one for cleaner activities. I purchased the HR version because it can be synced with the regular Charge.
There are many reviews discussing the inaccuracy of the heart rate, sleep hours, or step count, but if you realize it’s a wrist band and use the data to show trends and general activity level, it’s a great product. I do have a chest heart band and have determined the HR tends to be pretty close, 1-4 beats different from it. Generally under. It also shows much fewer calories burned during active exercise than the chest band. For me I’d rather under estimate calorie burn than over.