I currently run the sliding Mp5 stock from metadyne industries on my A5. I paid about 90 dollars for it from the metadyne companies website.

As far as looks, i feel there is no other stock that matches it, except maybe for the Rap 4 sliding stock.

Function, plan on getting a riser if you want to use a scope or red-dot or anything like that.
It is easy to change the positions once you are used to it, but it will take a few seconds to do so, and you cannot do it readily in the middle of a shoot out, if for some reason you needed to.

Hope this helps,

As far as i am concerned i wouldnt have any other stock for the Mp5 look
-Oneway

I have the sliding stock if you check out the gallery thread titled my super killer mp5 moded and you will see it there. The stock is very solid and unbelievably cool looking the only problem is that you will not be able to use the stock sights. You will have to use a riser and then add a holographic sight or red dot. Even without a mask it is hard to use the sights the stock is too high on the gun. For cqb this is fins since you may be shouldering the weapon as you clear rooms, but for woodsball I have to put the stock all the way in in order to aim it right and then you might end up scratching your mask on the back of the stock like I did. I bought a riser that should help the aiming. I like it alot , but it is not fully functional for aiming out of the box. You might want to look at any stocks that tilt downwar from the rear of the gun that way you will have room to aim even with a mask on.

My Super killer A-5 MP5 moded