My wife and I also have both a Santander 123 and Lloyds (Club not Platinum like @jeff2001) current account. We will be keeping the Santander 123 for the short term savings interest on our balance and the cashback on a subset of our direct debits offsets their account fee. I plan to ditch Lloyds though as I don’t use any of the Club benefits and it is only the credit interest that really benefits me (leaving joint account issues aside).
User experience-wise, the Lloyds app is OK (it has touch ID login now) and makes online banking a little easier than just using a normal web browser, but no instant notifications so you have to regularly poll it. The Santander app is annoying to log into (3 of 5 digits from a pin number…) and is not as nice to use as Lloyds once you are in, but I can do the basics of viewing balances and transferring funds which is all I really need to do. Again I have to poll it for my current balance or wait for my weekly (!) text message giving my balance.
In terms of loss benefits with Lloyds Platinum, it is worth checking that you are really getting the best value from the benefits for your monthly fee. After being a member of their older Silver account for a few years I decided that I would rather choose the specific insurances I need separately after scanning the market (and maybe getting some cashback while I am at it) rather than trusting my bank that I have the best deal for my personal circumstances. That said, I think in the future, Monzo are planning to offer some extras like this through third parties, but as others have said they are currently focused on making sure the basis of the current account are stable and ready for 400,000+ customers.
I am personally looking forward to watching the current account evolve over the next few months and quarters and am happy to be part of an exciting journey. 