I have the latest TomTom app on my iPhone 6+. It really is very good and beats the Via 135 in terms of smoothness of graphics, i.e. the dynamic zooming in and out and when you turn (I use 2D mode), also the responsiveness of the touch screen on the Via can't be compared to the iPhone. TomTom looks really good on the high res iPhone 6+ screen.
As said above the Via does have a very good speaker, however, the speaker on the iPhone 6+ is very good too - much better than previous generations.
When I use TomTom, I have my iPhone connected to the car's USB connection and the guidance comes through the car speakers just like a built in sat nav - I think you have to have the iPod selected as the audio source though - not sure if you have to have music playing or not? I had music playing via the Spotify app at the time and it worked fine.
Traffic and speed camera locations are separate in app purchases (monthly or annual). Mine is mounted with the Kenu airframe mount (recommended to me by another Civinfo member), it works very well in the 9G and while it is expensive is a quality product - you can even keep the case on your phone. Make sure you get the 'Plus' version if you have the iPhone 6+ though.
I have found that the TomTom app can seriously drain the iPhone battery if it's not plugged in, it can still drain the battery while plugged in, but at a much slower rate. You will have to turn the screen brightness down a bit from max and maybe close down some background apps to ensure the iPhone charges, or at least maintains battery level while using the app. The app does have a power saving mode, I've not used this though. (https://en.discussions.tomtom.com/to...y-drain-909013
I've had the TomTom app for a few years now, used to use it on my iPhone 5 all the time. Since getting my 9G, I have not really used it as mine has the Honda satnav which I also find to be very good. For a change I used the TomTom app again earlier this week and it was still as good as it always was, just looking even better now on the 6+ larger screen.
Let me know if you have any more questions or want me to check anything for you.
NB: just thought that if it is the case that you have to have iPod selected as the source on your head unit to hear the guidance (as I believe you do), you won't have guidance when you listen to a CD or radio and I don't think you can tell the iPhone to use the built in speaker when connected to the car's USB as it sees this as a 'dock'. To charge the iPhone and use the iPhone's built in speaker you may have to power the iPhone using the forward power socket (under the flap in front of the drinks holders), for which you will need a USB adapter. Hopefully another member can verify this, failing that I can go to my car, plug it in and play around.