518 uses AA batteries and has all the features of EXPS.
http://www.eotechinc.com/holographic-weapon-sights/model-518
Price: $539
558 is compatible with all Gen-I-III night vision devices and features an adjustable, locking quick detach mount
http://www.eotechinc.com/holographic-weapon-sights/model-558
Price: $629
