If you'd been following the thread, you'd see that the majority of posters may see an error a time or two, but that the transaction does go through. Even I have trouble sometimes, but it comes down to how I hold the phone in relation to the reader.
I've read through this thread in its entirety. The fact that there are people posting positively about it on this thread is in no way indicative of the actual real world success rate.
Even if in many cases it does work, what about various regions? Do certain financial institutions institute it badly?
I get payment failures rather frequently. With that said, I've had more than 50 successes in May alone, but the payment failures are at the point of authorization. In other words, I've done everything right up to that point and it's now out of my hands and then a message comes back such as, "Card not allowed," or "PIN busy, try again later," or my favorite, "Invalid security code."
Samsung Pay has yet to hit any sort of critical mass to really know how successful it is. In numerous reviews on youtube alones there's usually at least one transaction where the person has a failure at the point of authentication.
A good old fashioned debit or credit card doesn't do that, and it's important people about to try this thing out realize there are still some serious bumps with it, or there CAN be and sometimes it's completely out of your hands.