I fell in love with the KH310 at the first listen back at an AES convention in Berlin. That week I had the chance also listen to the 420 + 870 combo, the best sound system I ever experienced yet.
The upgrade from average two-ways monitoring speakers to the KH310 was life-changing for me. It simply sounds right. Immediately. It takes some time of course to understand the details of these speakers offers and the difference to your former set-up but you'll feel that you can trust them.
For me the main point that is unequalled by any other manufactures on the price range: the woofer. The low response is precise, tight and clean; I realised how distorted the low spectrum and smeared the transients are in 99% of the set-ups I know.
As a music producer, it solved my issues for the mixes I was struggling with, since you hear everything with precision, it is simple to just pinpoint what is the option you prefer and want.
As a music lover, the well-produced tracks will sound like nothing before and shivers will be there. Unfortunately, less well-produced pieces won't make the same effect on you anymore. Also since you can hear everything, subconsciously your brain will be more active and it is less "relax listening", more tiring.
One star less for the very basic spectrum control shaping in the back of the speakers but any good DSP or DAC will allow you a precise control beforehand for professional set-ups.