FYI, using this on an EM1, not the E99 mentioned above.
After getting tired of having a drop from using the E99 (which has a CIP Tuc Tite II) i purchased this for my EM1.
On/off feature is great since no one likes that burst of air coming out when unscrewing the tank. With the way i hold my marker, having an asa directly on the grip lets me rest the tank on my shoulder or against my arm, letting the back of the marker rest against my mask for improved aiming. Keeps me nice & tight behind bunkers.
Mounting takes a bit of time, though. First, remove asa by loosening 4 set screws. Second, line cage holes & cage screws to bottom of grip. The screws came with a drop of blue loctite on each one so tightening took a little more work than usual. Third, slip asa back into cage but before tightening the 4 set screws, put on a line fitting (when screwed in completely, the fitting butts up against the cage). Finally, tighten the 4 set screws (which also had loctite) until the asa is secure.
This is a good upgrade for anyone looking to ditch the drop. Even makes up for the time spent mounting it.