This is one gadget that most new digital photographers tend to miss out due to the the digital review on the DSLR. During the film days, this is one tool that a professional photographer needs to have in his arsenal so as to get the light reading right on spot before the actual shooting takes place.
Now what we can see most photographers do is that the shoot, view through their LCD screends, make necessary adjustments and shoot again. So much easier. Then again, this small gadget is very useful for metering the amount of adjustments needed before the shoot and waste shutter clicks.
Ah well, different opinions amongst photographers may result in diverse use for this gadget. To me personally, the flash meter has been with me for more than 10 years now and it's still being utilised for some detailed shoots at our Ipoh Photography Studio.