Packing: It is almost impossible, securely packed, yet easy to open. No gravity, no wrangling, all easy. Here 5 of 5 stars.
Processing: For a headset this category (type, price) satisfactory. Everything looks solid, nothing wobbles. The connections are ehr a little too tightly. Rubber / plastic of course, solid with good design. Hinge for adjusting the ear clip is also great. I suppose it would survive a few falls off the table, it will not enforce. 5 of 5 stars.
Headphones: Fits comfortably on the ear, does not slip, not jammed. I'm wearing glasses and was therefore skeptical here. For small ears may be too loose, but only suspected. Sound quality is very good for a standard headphone, more can not be expected, of course. Personally, I liked right "in-ear" better, so 4 out of 5 stars.
Microphone: After connecting initially shocked. Windows receives only a whisper, even when I hold the microphone to his mouth and talking loudly. BUT: here you have a little fumble in the configuration and turn up the microphone boost. If you have done this it works as expected. And the sound quality is great. Even with full boost of 30dB interference will not. In Skype Test class quality to me was confirmed. But as I think bad the necessary configuration, particularly with regard to inexperienced users, I draw here from a star overall. 4 of 5 stars.
Comfort: The longer I wear it, the less I notice it. Of course, you noticed it when care is taken. The spectacle effect, aka "Where is my headset" is probably not occur, but it does not bother absolutely. The control for volume and mute can attach a clip to the clothes. 5 of 5 stars.
Conclusion: If the Sennheiser PC 121 is configured correctly, you have a high-quality headset with good comfort, which is also suitable for eyeglass wearers. I can recommend buying a good conscience.