Hello!
You can use any of these for monitoring heart rate. If you are not comfortable then get yourself monitored by a physician or a para-medical expert every 6 months while at rest and also after a cardio. It is always good to monitor it yourself.
You can go strapped or strapless. Some versions contain heart rate monitor chest strap which are better and you can choose one of these.
Take care!
sorry hit send by mistake i mean a heart rate watch etc without the use of a cheststrap to show rate