That is the gain bandwidth product figure. That means that at 1MHz you can get only gain of 1 i.e. a follower and not more however you may try, at 500kHz you can get gain of 2, 200kHz gain of 5 etc. This figure also is taken at a very small signal amplitude, so that the output waveform is not afffected by the slew rate as slew rate is important for large amplitude signals.But didnt datashhet says "Wide Bandwidth (Unity Gain): 1 MHz"?
1. If 1Mhz is not freq to which it can operate, then what parameter define what max freq opamp will work fine?
2. Otherwise why 1Mhz is mentioned?
You want a comparator, so you want the gain to be in the hundreds or thousands for it to be useful. That would mean limit of useful operation somewhere about 1kHz-10kHz.