I use the PMX680 Sport, recently upgrading from the PMX70 Sport (which I also still have).
The PMX680 Sport sounds fantastic, for what it is--and what it is, among other things, is a fitness headphone that you can sweat on profusely and then rinse under water (like the PMX70 Sport). I believe it uses a 14mm driver that is similar, if not identical to, the MX W1 (the Kleer wireless Sennheiser earbuds). In my opinion, this is a gem of a driver. In my review of the MX W1, I said I'd love to see them use that driver in a wired product, and it appears they've now done that with several products, including the PMX680 Sport.
The PMX680 Sport sounds significatly better than the PMX70 Sport, too (to my ears), with better balance, and more extension. I also find it to be more comfortable on the head. (The PMX70 Sport was comfortable. The PMX680 Sport is just more comfortable.)
Now, the one negative: If you use an armband to hold your iPod (or whatever player you're using), then you're going to love the cable length. If you don't then it's not quite perfect, but still fine. The reason is that Sennheiser designed a two-piece cable, the first length being the one directly attached to the headphone itself. That length of cable is perfect for an armband, leaving just enough slack in most cases to be comfortable, and no more--again, it's perfect for that mode of use. But if you attach the second part of the cable (that contains the volume control), then the volume control's mass might be an irritant, if you've got nothing to clip it to. I would like to see the cable changed so that the first length remains the same, but the volume control on the second length placed lower on that portion of the cable. This would, however, necessitate a redesign, as the volume control is currently also the cable connecting point (the connector and cable connecting point would have to be separated to accommodate my suggestion, which I think would be a good idea, as it would also likely result in the volume control being lower mass).
All that said, I don't use an armband most of the time, but still choose the PMX680 Sport over the PMX70 Sport every time. Why? It sounds better, is more comfortable, and I'm able to remedy the aforementioned cable issue by clipping the volume control to a fold of whatever shirt I'm wearing.
Is it worth it? The PMX70 Sport is something I've had for years, sweating untold gallons of sweat all over it, and rinsing it with untold gallons of water over the years--and it still works like it did on day one. If the PMX680 Sport is as durable, then I'd say that it is definitely worth it.
Sennheiser is a long-time Sponsor of the site. (While this doesn't affect my opinion one bit, it should be mentioned, in case it affects your opinion of my opinion.)
