Flat top rail looks cooler but is not very user friendly and in the end will not be as ergonomic as the carry handle. With the flat top an optic will have to be mounted very high for proper cheek weld. The handguard and charging handle do two things: they allow for true back up irons and true ambi charging handle. All you would need is a picatinny adaptor and a lower mount optic (aimpoint micro, etc...) and the carry handle becomes much more attractive. With the flat top mount shown in the pics there is not much space to mount an optic, meaning you would probably have to ditch the irons for the optic. I'd prefer to have back up sights.