It's a bit weird, having to run pretty slow, to maintain a low heart rate, but strangely still very enjoyable. I wouldn't say it was uncomfortable, but it takes a while to get used to it. When running at this pace, I find I can run with my mouth closed, breathing entirely through my mouth. I can't do that at my previous pace.
Following advice on here from
@Stuuuuuu and others, I thought I had already slowed down to a 'conversational pace', but often found myself out of breath, and unable to converse if I had a running partner. I got home, then walked up and down our street for five minutes, getting my breath back.
This was the second time out using this method. It has added around 2 minutes per mile, but I'm not fussed about that. The run itself was more enjoyable because I wasn't feeling exhausted or out of breath at all, right through to the end. From the little I've read about it so far, my times will improve as I become more accustomed to running in the aerobic zone.
So I'm going to stick with it for a while, and see where it takes me. I'm 58, so my running is totally for fitness and enjoyment. Run times are a very low priority.