I’d say the two options have a comparatively computational cost, so really it comes down to your workflow!
The fanned box method will be slightly cheaper, but at this scale a simple convex hull collision as you have generated is also perfectly sufficient.
However, hand placing all those boxes takes time, and time is everything when making your game. So if you find those convex collisions quicker, I’d highly recommend that!
If this is a static object in your scene, the custom tool method is fantastically well optimized, and for most games this would be more than sufficient. Frankly, I think it’s the perfect balance between optimization and a quick workflow!