Main enhancement for me was Glonass + GPS satellite support which gives you a very quick fix and claims of better accuracy in trees. The fix is quick, but the accuracy is no better than my phone in my experience.
Bluetooth is the other major feature. It never works for me. Plenty of others on the Garmin forums say the same. I can pair anything to my phone no problem except the 510.
Yeah has touch display. Not really fussed with that, and I do find I have to press the screen a couple of times or harder to ensure it registers the touch and the touch resolution is low so it sometimes resisters a press on the wrong place. No biggy really though. I’m glad it has an option to lock the screen if you place it in a bag, as I tend to do.
I’d consider the 800 also. Lacks the new features, but same price as the 510 and has maps.
Performance pack I got in a deal though personally I don’t really track performance as I don’t race or do any road. I don’t bother with the HR strap now as it’s nothing but curiosity for me. Cadence is of no interest to me off road. Speed sensor is of use, although for Strava use it’s more accurate than GPS speed but tends to place you slower than others purely because it’s accurately tracking the actual ground covered not location distance. The pack comes with the combined speed and cadence sensor and I find it can get knocked about easy off road. I’m thinking of swapping it for the magnetless speed sensor that attached to the hub.