Stingray II is similar in that it is a polymer gun, they are comparable.
A sling, perhaps a better barrel, but you can mod the one that's on it. A foregrip, has to be handmade though. A bottomline if you want it, but not really neccesary.
INEXPENSIVE, easy to work on, solidly built.
Slow rate of fire, not fit together well, hard to cock.
Alright, I picked this gun up for $25 at Academy, and I bought it as a beginner gun for my girl, or as a backup gun for me. I brought it home and completely disassembled it. It's solidly built out of a thick plastic and it's got a lot of metal parts in it too, so don't be fooled by the fact that it's "plastic".
Alright, so what I did to it was: I first of all ported the barrel by drilling a series of holes into it about every three quarters of an inch, then I smoothed out the edges caused by the holes and then polished the barrel. I polished the lower portion of the bolt (metal), and then sanded down and smoothed out the upper portion of the bolt (plastic). On the face of the bolt that strikes your paintball, you have to be careful, because there can be (there was on mine) a little lip, edge, whatever you want to call it, of plastic that would cause severe ball breakage. You can also smooth out the bolt face a bit and round it down a bit more. Also, on the front of the gun, there is a big screw that fits into the gas chamber, remove it and make sure you really lube the gas pin, otherwise you'll leak CO2 or air or whatever all over the place. I also polished the sear and trigger realease. On the metal bolt housing, make sure you file down all rough edges, otherwise when you start using it, little flakes of metal will get rubbed off and can foul up your gun. The feed tube needs to be filed down as it has a semi sharp edge surrounding it. The elbow that come with the gun needs to have a small hole drilled in either side to allow the gas to escape but don't drill it more than a 1/4 of an inch otherwise you'll risk weakening the elbow. Finally, just make sure you lube the gun up really well.
I also made a foregrip for this gun, for an idea of how, see my review on my victor. With the vertical CO2 tank, and the foregrip, it looks slightly like an MP5 or other SMG.
Finally, for a sling, just buy a utility strap from the camping section of wal=mart for like $2, feed it through both the front and back of the sight rail, secure it, and then pull it tight against the sight rail.
Even with all the mods you can't fire too fast, because for some reason the balls don't feed super fast, and if you get ahead of your rate of fire you end up shearing one in half and that's NO fun in the middle of a game. I suppose if you used an electrical hopper, it might solve that problem, but having an electrical hopper is just one more thing that can go wrong in a game.
I'd say that if you know how to work on guns, or want to learn, this is a good gun for the money. I believe it's been discontinued, but a lot of places still have them, or you can find them on E-bay. I would say not to pay more than like $25, cause if you get up much higher, then you can go ahead and buy a Victor for $45. If you're wanting to learn, then once again, buy one, cause if you mess it up or something, then you'll have only lost $25. It's good to have as a backup or a loaner. I'm very impressed for the price.