I think SPD is far better for gravel. The shoes are way more walkable, the cleats last longer, they handle mud better and the shoes are far more walkable. I use SPD on the road quite often because my knees don’t like road pedals as much, but I can definitely tell the difference and wish I could stick to Keo/SL pedals. As mentioned above, my feet feel much more secure in road pedals.
I use toe covers on my mtb shoes, but they do wear out much faster as the lugs /contact points wear holes in the bottom. I just put a new set every season.
As others have mentioned, I’d buy the far cheaper Assioma MTB pedals over the Garmin.