I haven't used the 530, have a 520 and recently bought a Bolt after being fed up by issues with the 520, with the last straw being a well-known issue where the Varia radar will stop reporting if the unit drops the BT phone connection even if it reconnects. I saw the same issue reported on the Garmin 530 forums, so Wahoo won by default
There are only 2 things I like better about the Garmin: Di2 hood buttons are programmable (Wahoo only maps them to the physical computer buttons) and profile support lets me move it between bikes and not have useless sensor fields.
Everything else I like better on the Bolt, though the 530 might be more competitive than the 520. Battery life, UI responsiveness, screen clarity - yes even maps are easier for me to read. Also notable is that the Bolt supports workouts and displays more info about intervals, while my 520 only showed the interval type and power range.