I think you are entangling different issues:
- The risk and hassle of dealing with two phones;
- The risk of exposing your real identity to random escorts;
- The risk of merging your two identities and perhaps sending a punting note to a personal contact;
- The risk of being caught punting by a partner who might read your phone;
- Cost.
Since these are different for all of us, the 'right answer' is not the same.
For me, I don't care about cost at all compared to the other things. If it is equal, sure, I'll save money, but first I do what is safe.
For me, the risk of having to explain 2 phones is ultra high. And the hassle of two phones (missing a note from an escort I wanted to read, taking the wrong one, charging two etc) is pretty high too. The 'rule' to have a punting phone was based on 2015 technology IMHO. With 2026 options, I find it safer to just have one phone and to manage it like James Bond. I have a Hush second phone number in it. Second WhatsApp in it. No overlap of contacts. I also need Line (Thailand) and Telegram (Spain) and WeChat (China) which need to go on my main phone.
I used to have 2 phones. Now I have one. Overall if my main phone is unlocked and read through by a partner, I am probably well and truly scuppered. But I prevent that. I have one phone not to save money nor to be lazy, but to stay safe the way things are for me.
And in fact i might survive an unlocked phone read. There are extra passwords on all my punting apps (Hush, Line, etc.) Not sure that extra layer of defense would work - and I hope it is never tested. Hmm and I have a Revolut App for my punting money - that is basically another punting App.
For you, if you put WhatsApp business (aka WhatsApp punting) on your personal phone, you are already merging them and trusting passwords etc. That somewhat defeats the benefit of two phones. If you trust it (as I do), the second phone is perhaps a liability, not a benefit. One well defended path might be better than two medium defended paths.
I appreciate this is different for others.