I considered a third party battery too. After I read so many negative comments as well, I just opted to buy an original. My last one has lasted over 400 cycles, while Apple only guarantees 300 and it had never let me down, no overheat, no warping of the pack. So, I can't say from experience that you shouldn't buy the fake one, but I would recommend you that you don't.
Sometimes taking the seemingly 'cheap' path turns out to be more expensive than doing it right the first time. I've had that happen so many times that these days I opt for the second option whenever I can.
Hope this helps.