Sorry - I don't understand.
Clearly

Why would anyone pay 'just' £25 for something which is crap? Full Postcode Entry? Traffic Updates? Realtime Redirection?
I get all that from a FREE app on my gayPhone. The built in Nav on NCDC is shite. It was on the day it was released, and it is today.
NCDC works. Well. Very well. Despite 15+yrs old, it outperforms *any* portable unit hands down. End of.
Granted, it lacks the gimmicks of modern units (but is 15yrs old).
It is actually outperformed by the even earlier CARiN units, which will still work well for miles after unplugging the GPS aerial. Sadly the bloody thing is too slow with reasonably modern maps. Your stupid portable unit will go apeshite the second it goes to below 4 or 5 satellites. Hence my last portable unit is at the end of the Aston Expressway, and the previous one lost an argument with a heal. They are complete crap. And then there is the hardware/software reliability.
Most portable units are marginally outperformed by modern mobile phones, but if it wasn't for the fact these have other uses, they'd be smashed up as well.
BUT nothing comes close to a proper built in system. Not even close. Gimmicks like postcode can be useful, but ultimately pointless if the thing lets you down when you need it most.