The choice between a low and high battery compartment in Aimpoint models like the CompM4s/M5s and CompM4/M5 often comes down to personal preference and specific use cases.

The low battery compartment models, like the CompM4s and CompM5s, offer a slightly less obstructed view above the optic, which can be beneficial for maintaining situational awareness and peripheral vision. They're also a bit more discreet and can be easier to access with the right hand.

On the other hand, the high battery compartment models, such as the CompM4 and CompM5, are often preferred when using magnifiers or night vision devices. The higher position makes it easier to adjust the dot brightness without obstruction.

In terms of durability, some owners feel that the switch is a bit more sheltered on the low battery compartment models, potentially reducing the risk of accidental adjustments or damage.

So both designs are there to cater to different preferences. If you prefer a cleaner sight picture and don't plan on using additional optics, the low battery compartment might be the way to go. If you're using magnifiers or want easier access to the brightness control, consider the high battery compartment.