You being a runner, have a very good idea of long term effort. What you likely do not know is in cycling how long/how much lactic acid your legs can handle and how it equates to running HR (cycling is lower).
It might be good to start recording. PM are very popular and to suggest you can do as well without them generally starts arguments. But there are some (rare) that do just fine without them. They tend to be the type that can guess their HR, effort, speed and power based on experience. For someone like you I think recording early would be good.

I'm not thinking they are as important in racing, or so much for experienced trained riders.