I don't know if it is an older model or not. Mine looks like that one.
The Eotech magnifiers are going for around $550. A quick detach base is going to run around $150.
I have no knowledge of the Strikefire sight.
The Eotech magnifiers are designed to work with the Eotech series of sights.
My first optical sight for a DPMS Panther is an Aimpoint and the magnifier behind it is an Aimpoint.
I mis-spoke when I said I have an Eotech magnifier. It is not. Mine is Aimpoint.
That being said, the unit seems identical to the Eotech magnifier.
I belive L3 is a conglomerate of companies and I am not sure of the relationship, if any, between L3, Eotech and Aimpoint.
I am not sure if any of this helps or not