I originally used the regular end to end stretch type covers but went to flip ups years ago. They are so easy to use that I cannot fathom how they would get in the way or cause a fumble.

I flip them up the moment I suspect that a deer is in the area. Only significant rain or snow will delay that. Any cover protects the lenses but, unlike see throughs, flip ups do not collect the same debris that the actual lenses would. Your sight picture is inhibited whether the snow, rain or debris is on the lenses or lense covers. No benefit there. If the covers are messed up, you might have to take them off in the field; maybe at the wrong time.