Today I received some WS2812 leds for my next project. It are ledmodules without wire so all connections should be soldered manually. All connections pads (6/led) are sold pre tinned (some with terrible soldering skills). I paid 106 US Dollars for 500 smd5050 ledmodules (hope I will have a lot “pixel fun” for my money :-). Does anyone have experience with these little pixels? Do you think the price I paid is good?
I bought 1000 of those a while back and while I have used a few here an there, I have not yet tied a lot of them together. They work great so far! Perfect for adding a status RGB to your MCU. I have not yet accidentally reversed polarity on these and the +/- are difficult to see. I imagine it will happen and I hope they are the protected “B” version. These are destined for tuxedo coat project!
I doubt those panels were hand tinned. It’s more likely they went over a solder bath to get all the pads tinned. Without anything sticking out on them (like a through hold leg), the solder has nothing to adhere to other than the pad and sometimes it will bridge and connect two pads together. It’s the nature of the beast.
I have 8 of these panels soldered up as a 80x10 matrix. I actually gave them all a gentle rub with wire wool before hand tinning each connection as I had a few on the first panel which didn’t flow so well when soldered. I used solid copper AWG18 wire for the power rails straight across the pads, but only soldering 1 connection per led. This reduced the count to 4 joints per led 
I did post a while ago after I had soldered up one panel for testing.
I managed to get most of mine for $18 a panel. So $21 a panel is ok, several sellers charge a lot more.