I used my 520+ again after being on the HH for about 18 months and holy crap, the Garmin UI is so bad in comparison. Having something as basic as PM calibration buried several menus deep is just silly.
User experience on the Karoo2 is really nice. The WiFi upload vs BT is the only real friction point for me, have to use my phone hotpot to upload a race file sometimes. But not a terrible trade off for being a lot more pleasant while actually using it.