As far as the physics are concerned, it will only get you a higher fps. It shouldn't get you more accuracy. I will let someone else explain why (*cough* Cheese *cough*) because my explanation is pretty rocky and I probably won't get the whole thing. So unless you ae looking for maximum fps, it's not worth it.
Don't get it! basically, the 430mm inner barrel is pretty perfect in terms of cylinder volume for VSRs. I ordered a PDI outer barrel and they sent me the 690mm version which is for the 554mm inner barrels, but I'm keeping my 430mm inner barrel inside it.
A huge mistake people make in airsoft is thinking that the longer the barrel the more accuracy you will have, it isn't true. I've seen pistols out-range assault rifles!
I read somewhere that the best barrel length (for maximum power, accuracy will be the same) for a vsr-10 cylinder is 500-510mm, assuming you have good compression. So, that 554mm barrel won't give you much of a power advantage. Accuracy will be the same, if not slightly worse because the piston will hit the cylinder head before the BB will exit the barrel.. i guess you could get a bore-up kit with that 554mm in order to maximize power efficiency with heavier springs/bb's, but even then there's only a small advantage in fps. And with fps limits, why spend the money? I'd rather save the money for far more important upgrades.