The older Eotech designs with the batteries parallel to the barrel have issues with recoil disconnecting the batteries and damaging the battery contacts. The newer ones have the battery perpendicular to the barrel and do not suffer from this issue.
I have two with the parallel batteries as AA batteries are cheap and plentiful. If the SHTF, don’t want to be searching for CR.123A’s.
At least that was my logic.when I bought them. That and the 552 has the only 308 specific reticle.