If it was me, I'd just buy a comfortable day pack and use it as a storage area for things on the top of the rack while riding. I doubt any of the convertible panniers will be that comfortable to wear, you can't bring all your panniers along on the hike anyway, so why have all the extra stuff/straps on them. You can even pick up one of those lightweight day packs with no backpad that folds into a little pouch or just a fanny pack that doubles as another bag to hold things while riding. Really depends on how serious a hike you'll be taking, but I think all these are a better option then the convertible pannier.