Thank you very much for this thread Big cats it has been both very interesting and informative for me.
Forgive me please if I ask seemingly stupid questions here but I'd like to get this all straight in my own head.
Four of us will be touring in the Balkans over three weeks in June. Looking at the Airolo app (thanks Martin

) I see that I can get a Regional package with 10GB for 30days at $37 which will cover all but two of our countries. I'd imagine that all we'd have to do is activate the e-sim and go but am I correct in that assumption?
Can I have a second e-sim on my device (Google Pixel 8 Pro) so that I can get a Local e-sim for Bosnia with enough data for a couple of days? I'd intend to leave the physical sim card in the phone and use e-sims for the trip.
Would you think that 10GB and an additional 2GB for a couple of days in Bosnia would be enough to allow me to use Google maps and WhatsApp (I don't intent to be making or taking calls otherwise)?
All the world and EU coverage with 3 for the 21 day duration was going to cost me £90 but I think I will get data for all countries for $44 (£35) which is a significant saving. Again thank you and Martin very much for all the information in this thread. I appreciate it greatly.