Many Different Modes of Firing
Adjustable Rate of Fire (on Auto)
Long Battery life
Requires tools to make adjustments
Difficult to see what setting you are on
Well the E-Grip is a nice option to have if you want a variety of modes of fire. You can shoot a single shot, a shot on the pull and release of the trigger, 3 round burst, full auto...etc. Also you can adjust the rate of fire (ROF) for the full auto feature.
Now for a bit of the downside....I have had some trouble with different batteries fitting flush inside the E-Grip, a rechargeable one i got the other day wouldn't even slide into the niche for the battery. Also my most major gripe is that it requires tools to select the mode of fire...and it is very difficult to see what setting you're on without discharging the marker. Lastly the E-Grip unlike the A-5 Receiver/body is made of Plastic, not a real complaint but just an observation.
Also through personal experience...i bought the E-Grip used and it came with a battery already installed in it. I'm not certain if it was new or had been used a bit, but the battery has gone through at least some 4-5 thousand shots fired; and is still working. So, while I'm not certain what the actually life of a 9V battery is in an E-Grip, it seems pretty lengthy.
The E-Grip is a nice addition, but at the price ($100), it is not a necessity. I have rarely used the full auto feature (not my style of play), but I suppose if you would like to have that kind of rate of fire available then the E-Grip is your choice. I wasn't terribly impressed, but i like having the other options available, and since I bought it I'll stick with it.
But if i had a chance at a "do over", I would have taken that $100 i dropped on the E-Grip and invested it in either the Flatline (#1 choice), a JCS stock w/ RVA, Lapco Offset w/ 42mm Red Dot, or a HPA tank of some sort.