It's got everything a back player could want, speed and accuracy. Depending on how old it is, it might a gas hog, so make sure you've got the right tank for it.
Shocker with a good tank is a good choice for back. In most rookie events, you probably won't be throwing as much paint as some of the more experienced teams, so efficiency shouldn't be a big problem (unless you're playing 10 man rookie )
Although I have a shiny electronic bling-bling machine as my main marker, my Shocker still comes to every tournament as my backup. Gotta love Shocker accuracy.
I own a shocker and play back, if you are using it on CO2 wear gloves, cos if you fire a full tank ( about 800 shots ish) then your gun can get ice on it and you do stick to it! a bottle cover too as they tend to freeze.
It's a greatly under-rated marker that's had it's fair share of ups and downs, but I'll never give mine up. Whack on a decent airsystem and you're pretty much sorted. Obviously steer clear of the Turbo mode to keep popular with your local site operator. Click the link on the bottom of my thread to read the ongoing saga of my quest to rebuild my Shocker. Enjoy.