I do - I have both Irish and British citizenship - and before Ireland joined the EU and we all got the same passport, having an Irish passport saved hours standing in the British passports immigration queue....

coming back to the UK on a package holiday flight at the same time as loads of others, meant that the queues of U.K. Passport holders was far far longer than the one for "all other passports". I used to zoom through that one and be at the carousel collecting bags while the others queued...

with Brexit I can see it working the other way.... my British passport runs out just after we revert to a blue cover non EU one so I will have both again.....