Got the 42mm black band yesterday and I'm pretty happy with the purchase. Mine was shipped from FL to CA via 3 day UPS. By my estimation the band is about 30-40% thinner than the original Apple band, which actually makes it more comfortable to wear. The fit on my wrist seems to be comparable to the Apple's version.
I initially had the black Apple band, but quickly returned it due to the finish (coating) peeling off so purchased this third party band hoping not to have the same issue. The downside is that this MoKo band attracts a lot of lint (very noticeable on the black band) compare to Apple's, likely due to lack of the extra coating. Also this MoKo band is slightly wider than my watch so I have an extra millimeter or so sticking out at all four corners (evenly). Overall for the price this product is worth it.
Update: Well I spoke too soon. After taking off the band and trying to remount the bands, one of them developed a problem with the pin and won't stay put. I can slide it off to one side without pushing on the band release (see pic).
Update 2: After contacting the seller and leaving a somewhat negative review on Amazon, I was contacted immediately by the seller and they are sending a replacement. Their customer service seems prompt, which is very encouraging.
Update 3: My replacement arrived in 2 days via USPS. I gotta say I'm very impressed with this company's responsiveness to my problem. I wish all companies can be so good with their customer service for a $5 item. The replacement is in perfect condition. Although quality may be slightly less than Apple's band, price definitely makes up for it. I just wish they would release some more colors and will definitely pick up more in the near future.