1) if its got a 14mm threaded barrel, just check the direction of the thread (if when looking down the barrel, the top of the flash hider moves left to unscrew and right to tighten, its a positive thread. If its the "wrong way" itd a negative thread, i think ccw is negative and cw is positive, but dont just take my word) and buy a supressor
2) the mock supressor will not improve either range or accuracy, but as you said, its for cosmetic reasons
3) if the supressor is to cover a longer inner barrel, this will also not improve either range or accuracy noticably. You will see an increase in fps with the longer barrel, but may end up bringing this back down if your gun gets above your sites limit. And the accuracy is much better improved by using a posh hop system or barrel (quality of barrel is orders of magnitude more important than length, look at TM pistols)