I have one (ordered it from a guy on the Beretta Forum-RIC70506 who makes them) and if you get one, I highly recommend getting one of his. One reason is that he employs a steel insert/sleeve (pinned in) where the barrel/muzzle meets the comp which strengthens the comp and will give longer life. I am not saying it is best, but it is what I went with. I also believe he has a bunch on hand so there is no wait time, like from some other manufacturers. Something that is important to know is you might have to file/sand down some spots on the inside wings/tabs of the compensator due to the different widths of the Beretta 92 frames. I had to do this with mine. I never would have thought that would be an issue but learned that Beretta did not make one size width of frames. You can measure the width of your frame( the area where the tabs/wings of the comp. make contact with the front of the frame for stability) and he can size them for you. It is not hard to do and might be better doing it yourself as some times people screw up the measurement which can leave you with an improper fitting comp. which can cause you issues with your frame getting damaged. I looked around to find the best comp. and bought the one from RIC70506( look in the classified section and it will be at the top of the listings). He can make them for the 92 and 96, I believe and in black or plane matte finish for an Inox slide/pistol or two tone look. I have no affiliation with him but like his product.
Now, as far as if it is really needed, that is up to you. I don't notice any real difference with recoil compared when it is one or off. It looks cool and might be a little beneficial with follow up shots with the slight weight on the end of the slide, but it is a full size pistol and Beretta makes a solid gun that can handle the recoil/abuse.
Like I said, I bought one and really like it. I also added a few other items, mostly for looks-skeletonized hammer/trigger, grips, etc.. It is mostly for aesthetics, which is the beauty having a gun. Like the ar-15, it is preference based, as you can customize what you want. Check into what you want and make the best decision on the info. out there.