We are traveling to Dublin - Belfast - Edinburgh - Dublin in September and wonder whether E-sim is better than getting local SIM cards.
E-sims are certainly easier, imo. No need to insert a SIM card - all you do is activate it and change the settings. I used one for a month in Germany and it was inexpensive and was simple to use.
But having said that, who is your cell phone provider? Some give you free international data plans with low cost phone calls (for example, T-Mobile provides free international data plans depending on which plan you have). Verizon charges you either $100 a month or $10 a day (and AT&T is comparable, I believe). Some people like the convenience of that and are willing to pay more for it. I'm not but that's me. I switched to T-Mobile last year and am so glad I did. I had free international data while I was in Scotland this year and it was wonderful.
Second, in order to get an eSIM plan, you must have a newer phone (2018 and up) and it must be unlocked.
Third, some eSIM plans do not give you a phone number to use. Many do and more are following (Orange, Airalo and so on) but if you need a phone and aren't willing to use WhatsApp or FaceTime to call people, you may want a SIM card (keeping in mind it will be a foreign phone number).