I've got a bunch of
AB's... but I've never used the Grex, I had originally stayed clear just due to cost for an
AB with a comparatively larger nozzle.
I ended up getting the Iwata Neo Pistol-Grip (gravity fed) and I love that thing. I've primed a massive amount of nids without any hand discomfort hah.
One of my other
AB is an Iwata so it was an easy choice for me. Their customer service is outstanding.