That a-forme last/fit sounds similar to my preference. How did you find sole flex, Nordkapp/Malham vs Tethera/Fremington?
The level of flex in any boot mainly comes from a combination of the midsole which is hidden from view between the base of the boot and the sole unit and the type and thickness of leather used in the construction.
The Nordkapp and Tethera are very similar as the design of the Nordkapp was based on the Tethera. The flex or lack of it is about the same but the Nordkapp has the advantage of a higher rubber rand which gives better protection to the toe area at the front of the boot. I would suggest that both these boots are overkill for use on the Essex trails, woodlands and fields as both these boots are designed for higher level walking which is why they are stiffer.
The Malham and Fremington use different leathers and from my experience I would say there is a bit more flex in the Malham and it has more of a rolling action.
For use on the Essex trails, woodlands, fields where you walk I would suggest that the Malham would be a more than capable boot.
Obviously the sensible advice would be not to buy without trying them first unless you are absolutely certain that you can return them.
I would also recommend that you invest in some decent Gore-Tex or eVent gaiters. There's no need to spend a fortune something like the Trekmates Cairngorm GTX gaiters can be bought for around £20.