The 510 as a NAV system is also far from as good as it could be. I now run TomTom on my phone and functionality along with the integration with Google maps and MyDrive completely eclipses the OE navigation. I also don't think the 510 as a head-unit is very good in terms of sound quality but that's a personal opinion.
I agree about the sound quality, it's average at best. The OEM speakers are capable of producing better sound. With the Alpine's time delay and parametric EQ, you can get a really good sound! I used to play around with that stuff years ago, making sure the passenger side speakers had less delay because I was sat further away compared to the driver's side speakers......I was a proper stereo geek back then
It does make a difference though!
As for the nav, I've not run into any problems with that yet, other than it being slow to boot up and some recently built roads not being in the maps.
Does the TomTom phone app use GPS or 3G/4G? Apple maps uses the latter, which is not great when 3G/4G coverage in the UK is diabolical.....on O2 at least.