Another reason to have the 2nd,3rd and 4th axis set is that if you think that the fixed sights and some dovetail sights the mounting plate is square your wrong, I have checked a bunch of them at the shop and was very surprised at just how badly out of square some of the more popular sights are.

Some risers are not square eitherwhich will open up another can of worms when you try and sight in.