After using an after-market wireless receiver for the past many months with my S5, I finally took the plunge and went for the original wireless back cover from Samsung. They are finally in stock and my 50% code brought the price down to about 20 bucks, which is hard to beat.
The after market single coil two-contact receiver worked for the most part, but it had some issues. The phone had to be exactly aligned with my Nokia DT900 or else, it would keep disconnecting or going into a loop. Also, once the charge was complete, the phone would bleep like crazy till I took it off the plate. This was a major nuisance because the bleeping could not be disabled (I did not root my device for various reasons) - and the phone sits right next to my bed at night. Also, even though I got one of the thinner receivers, it still added a small bulge to the original back cover. I also think the phone is probably not as water and dust resistant because the receiver sits very close to the rubber gasket on the backside of the original cover.
The Samsung wireless cover was shipped promptly and I have been using it for a few weeks now. The cover makes the phone thicker - I do not have a concern with that because I do not use a case. With the thicker cover, the camera at the back of the phone does not protrude out anymore. Instead, the camera (and the flash/heart-rate sensor) are nicely recessed into the case. Coming to wireless charging, I find that I don't have to exactly align the phone on the charger anymore. As long as I place the phone generally centered on the pad, it charges without any issues. And when it completes charging, there is no annoying bleep bleep sound, so I am able to sleep better at night.
The phone still comfortably slides into my car mount clip. The cover also does not have my Wireless providers name, and strangely, there is no Galaxy S5 imprint either. Also, I find that the phone is more comfortable to hold, although I wish the cover came with some kind of rubberized coating instead of the same dimpled "band-aid" look.
Update: Forgot to mention, NFC worked fine both with after-market receiver and Samsung Wireless Cover.