Noise isolation/ fit compared to Piston2? Comfort?
Piston 2 (P2) is Very Light (sometime feels there is nothing in my ear if Music not playing) comparing ED-9 but during usage (No Running or Work out though) I didn't feel ED-9 is heavy or going to fall from the Ear or So... I used Medium Size Ear Tip with Both Filter which provide perfect fit & isolation , but some user may snuggest Small Tip for the Neutral Filter (Brass) to get perfect fit / isolation.
When Music playing Noise Cancellation is excellent - But if the music paused you can continue conversation with other people situated near you or same room...and so is the case of P2.
So ED9 is better than Piston 2 when it comes to sound?
This is subjective - I find ED-9 is better sounding than P2, The Difference is not that huge... with Bass (Gold) Filter - User with ED-9 and P2 get same amount of Bass & Treble - There is no change, but ED-9 can yield good amount of Mids / Vocal comparing P2....and with Neutral Filter (Brass) the sound of ED-9 goes to different category <--- This is why this ED-9 is so popular/ praise among audio enthusiastic.
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If you are into EDM and Bass Only - Go For Piston (as the comfort is proven fact for P2) and you also get complete remote mic with vol up and down - But if you care about detailing (with Tight Budget) - chose no other than ED-9.