They seem like really good rings. I wouldn't hesitate to use either type of Burris insert rings. I've had excellent results with the Z sets I've bought in years past. But shimming is something I won't do to a scope.
thanks for all of the replies, fitted yesterday.. - 40moa put me within 6moa elevation , 4 moa windage of optical centre instead of nearly 1.5 turns on the turret.