Upgraded from some aging HD 558s (which I loved). These are very similar with some refinements (more bass extension, flatter response).
Pros:
- Very flat response (sub-bass rolls off by about 5db, normal for open-ears)
- Light
- Relatively easy to drive
- Build quality seems the same as the 558s, as in they feel a bit wobbly and unsatisfying but they seem to survive pretty much anything
Cons:
- Noticed some casing resonance when playing low tones, but not noticeable when listening normally
- Clamping force is too high but all my other Sennheisers loosened up over time
- Pads are a bit too firm, the 558s are currently much softer in comparison, but I can't remember what they were like new
- I haven't had noticed the inner casing touching my ear, but others have, so you may want to consider that