The satnavs that I’ve used in cars are mostly OK. The ones I’ve used in phones are mostly awful. Some observations:
The official Apple Maps application for iPhone actually consumes power faster than a normal car USB connector can charge it. So on a long journey your phone can go flat even if it is plugged in. On the plus side, it does make for quite a good hand warmer.
The Google Maps application (which you switch to because the Apple Maps one kills the battery) has a navigation display that is obscured by appointments that pop up on the screen and have no obvious way of cancelling. This is great if you are on the way to a scheduled meeting. Not.
The Official Apple Maps app (which you decide to use for a short journey) just plain gets things wrong. Exhibit A above. Searched for the West Avenue car park in Filey, asked the phone to navigate me there. Got taken to a residential street across the railway from my destination. Rather than using the geographical location of the thing I’ve searched for (which it seems to know because it draws it in the right place) it instead navigates to the post code which covers an area including lots of wrong destinations)