Being using dual sim on my iPhone for awhile. I have 2 lines since my employer provides a SIM card for business situation. Good thing is that since we are using office 365 I do not have to install anything on my phone so not a lot is tracked. I have to say that for me is working perfectly. I have my business phone using the physical sim and the digital one is the personal one. I use iMessage for my personal phone and Whataspp for business since is approve by them to use that. For email as I mentioned I use Outlook app for my business calendar and mail and the stock Mail app for personal emails. FaceTime I use my personal phone number to be reached if needed. The way Apple did this integration I have to say that works really nice. For Contacts I have a bit of a mix but almost have the trick. I went thru all my contacts and chose the default line for them… However, if someone from work needs to contact me via personal (since I have friends on my work) then if the message or call is using my personal, the return call without needed of doing anything from me, the call is returned using the line used by the caller (this is awesome) .
Just thought to share this summary about how I use it, and my experience.
Hardware iPhone XS (Both sim are ATT, however my phone is unlocked.)