I have a single sim phone - Android - I have a PAYG sim bought with cash and I top it when I need to punt.
Some times, when I don't like my meet with the escort - I just buy another PAYG - in case- she didn't like me either
They are free in supermarkets.
Yes, you do need to manually delete call/text history - but that is the least - one can do.
The sim is so small - it's tucked in my work bag - that no body goes through - and sometimes, I struggle to find the sim, in the pocket, I keep it
I find it much easier than carrying a dual phone - hassle and also I have no reason to carry it - so would struggle to explain, why I have it.
The only downside is the topup runs out after a month - so it's need to be topped up again by £10.
I don't punt so very often .. so I just regard it as an extra £10 on top of my punting costs.
Edit: I use Tesco's - so unlimited call & texts and good amount of data.