I use both. I have my home charger set to charge off peak and the EV set to scheduled charging at the same time
I do the same Dave TBH.
99.9% of the time I charge at home from our wall box, using an off peak tariff.
The on and off times are replicated in the App in my phone and the head unit.
One day last week we decided to make an unscheduled trip.
We had sufficient range, but I just wanted to add a few more miles while we readied ourselves.
Of course the car is set to scheduled charge.
I tried turning off the scheduled charge from my phone which returned as as successful, but it refused to commence the charge correctly.
I then booted up the car and disabled the scheduled charge in the head unit and tried again.
This time it finally stated charging.
When we returned from our trip, I turned the scheduled charging back on from my phone.
Later that evening at about 10.30pm I popped into the kitchen and noticed that the smart energy monitor was displaying a RED status ?.
When I checked it was clear that the wall box had started charging !!!!!.
OH NO - What is going on here, my off peak does not commence until 1.00am !!!.
Bit of a faff getting it to stop charging, but got there in the end.
It was pure chance that I caught it in the act.
The following morning, I checked what was going on and for some odd reason, the times set in the App had defaulted back to a start time of 10.00 pm ??????.
Why …… I have absolutely no idea ?

.
This has happened once before.
I find using the App for critical settings can be a little bit hit and miss sometimes.
The head unit appears more direct than any losses that can be witnessed via your phone somehow ??.
I tend to go belt and braces now and perfectly match my scheduled charge times in the head unit with the App.
My off peak tariff is a low 4.5p / kw where my day rate is a spiteful 40p / Kw.
There is no way I want any issues when it comes to incorrect charge times commencing early and therefore charging on the higher rate of course ?.
Load it ( the scheduled times ) Lock it and leave it alone, is my strategy folks.