If the compatibility to a laptop or smartphone was important, why not just get the sensors and skip the head unit ?. But since you want the head unit as well, kind of doesn’t matter about compatibility, ‘cause you are likely to always be using the sensors with the head unit.
The Bolt is a good unit, very reliable, good support from Wahoo. The 520 is also a good unit, likely the most reliable from Garmin currently. Some of the reasons folks like Wahoo over other Garmins is no touch screens, which some folks hate. The 520 has buttons, so narrows the choice if you want buttons. Then it kind of comes to do you want color or B&W.
All this kind of really shows how close the units are and at that point $90 becomes a hard sell for Garmin.