Comparison
Here are some comparison pictures of the surface material. Even though the photos might suggest otherwise, the MM350 doesn't have a fluffy surface; it's just the colored dying playing tricks on the lens. The surface is quite similar to that of the QcK Limited, which isn't really surprising as they nearly feel identical. The Dream Machines DM Pad XL and HP Omen (which has the same surface as the standard QcK models) have a vastly rougher touch.
HP Omen (exact same surface as the standard SteelSeries QcK) vs. MM350
Dream Machines DM Pad XL vs. MM350
SteelSeries QcK Limited vs. MM350
Build Quality
I could find absolutely no issues with the build quality. The surface, underside, and even edge stitching seemed perfectly smooth and had no parts sticking out as there are no uneven bumps of any sort.