I have owned and used three different strap-on HRMs from Polar and Timex. Then I got my Fitbit Charge2 and got rid of them all. I compared my Fitbit readings to the chest-strap monitors and I found that the Fitbit does lag a little, but if you just want an overall picture of how your workout went (IE, time spent at peak, cardio, and fat-burning zones as well as total calorie burn), it does just fine. I also like that syncing it with the Fitbit app means I automatically have a record of all my workouts, and I can view the graphs in my Fitbit account. Plus it adds the workout calories burned to my base activity, and adjusts the number of calories I can eat that day based on the extra calories burned from exercise. I've been using some form of Fitbit since the thing first came out years ago, but always used a separate strap-on HRM until I got the Charge2.
It also will tell you what your resting pulse rate is if you wear it all the time and to bed, which I do, and keep a graph of that with an estimate of your cardio fitness. It will tell you your current heart rate at any time you tap it throughout the day. In fact, a close relative of mine who has a condition where she must keep an eye on her heart rate at all times (her resting heart rate is in the 90's!) relies on the Charge2 as her monitor. (You can set it to alert you if your activity level drives your heart rate over a specified threshold)
I love the Charge2 and can't recommend it (or any other Fitbit product that tracks HR) enough. It beats wearing a strap all day long (if you care about your HR outside of workouts) and does so much else too.