I drive around the highways and byways and backroads of the UK on a daily basis for work.
I used to rely on my TT but, TBH, now use the freebie satnav app with iPhone. I have a large data dowload allowance so the free pop ups are simply an annoyance but frankly, for convenience and availability of device on the hurry up, I have no complaints. Pick your own route over the longer distances rather than rely on the device though.
That said, I type in the postcode to get an idea of where I'm heading then switch the app off and rely on the mark one eyball and a swatch of common sense to get me there or thereabouts. If needed, the app does the biz for the last mile or so.
Its very limited when out in the country hinterlands but that is more of an issue with wider ranging postcodes than the app. As a backup for such scenarios I use memorymap (not cheap if legal) as it gives Ordnance Survey mapping for the whole of the UK and gives pinpoint position for yourself which is especially handy if lost in the hedgerows!