you sort of know if you need one i reckon. if your guitar is almost there and the top end could do with a bit of opening up they do work - not just with humbuckers by the way (i use one on my boss bridge).
you can experiment with what might happen by removing your tone control, or even volume pot. its not quite the same but it gives you an idea. if 1M doesn't work then 2M won't help you. think I have 1M pots on a couple of my collection. on many more guitars i went to 350k because it was sounding all too bright.
it doesn't affect the bass end, but it can give the feeling it does, you get more cut too.