It's hard to say whether or not an IEM is "worth" the money. The Philips SHE3580 costs 10 dollar. The Brainwavz M2 costs 50 dollar. Is the Brainwavz M2 5 times as good as the Philips SHE3580? It's very hard to say.
Most of the times it's not though. If you really look at price-quality ratio, the Philips SHE3580, Thermaltake Isurus, Monoprice 8320 or Focalprice CK-700 are probably the best IEMs to buy. But it's just very hard to compare IEMs that are in a different price range.
I don't own a panasonic hje120e, and although it looks good from the reviews I have read on head-fi and other sites, the Philips SHE3580 seems to be more popular. And I can ashure you that they are freaking good. Amazing bass for the price, amazingly comfortable for the price, amazingly small for the bass
. They don't beat the TT Isurus or Monoprice 8320 in clarity/detail/separation, but the bass is definitely more enjoyable. The bass even hits 15hz. Not that you can hear that, but you might feel it!
Just at the time I bought the Philips SHE3580, I discovered hip-hop group "Hilltop Hoods". All I can say is that the SHE3580 is perfect for that kind of music.
Oh, and about the Brainwavz M2. For the little time I had them (1-2 months), I loved them. But they didn't surprise me as much as the SHE3580 did, and my astonishment when I heard the TT Isurus was even bigger. I'm not saying the SHE3580 is better than the M2, because it probably isn't, but I guess I wasn't really surprised about the M2 because I paid so "much" for it.