Thank you for your replies.
For the record, one of my rifles wares Tally QD mounts. They are solidly made, the levers are 'robust' instill confidence thet will not shear off easily when tightening up / attching the scop / rings to bases. To my mind, the Leupold 'little' levers side levers look, well little. I can readily see me breaking those off when trying to fix scope. For this reason, I do not think I would go alimuminium over steel monts in a QD mount.
The issue I have is the Taley QD levers catch on things - slings, vegetation, clothing. So, I was wondering if a detachable version that requires a little tool would be better. I guess people carry a little tool kit with them when hunting away from hom. Maybe some action spare parts too?
I like the idea of some spare part insurance when hunting a long way / distance / time from home. Hence the question about having a back up, zeroed scope at hand.
The repeability issue question comes from my observation how the scope rings clamp / tighten on the base as the lever arm is rotated: how much off original centre will they be when re-attached. I like the look of the Conetrol mounts but these are more of a bench / workshop change out option - need tools and pretty precise repositioning using the sets of screws - must be turned back in by the same amount turned out to loosen / detach. Of course, this could be assisted by the use of witness marks engraved into scew heads and bases body.
The comments about hitting rectangular area / vital zone comes from seeing the Swarovski video for scopes with range finding BRH & TDS reticles. They were hitting steel plates at some quite impressive distances.
