I used plastic ones in the past. I used 1 gold riser or 4 around the cpu socket, and for the rest plastic ones. They're an even bigger pain when in comes to taking out the motherboard. You have to press the plastic bit in the center in order to pull the mobo out. And you only have 2 hands, you do one at the time and most of the time, the ones you already did snap back on, so you have to start over. And they don't last that much.
IMO it;s better to use the gold ones, tighten them with some pliers onto the mobo tray, put the mobo in and tighten the screws in the risers by hand or using
very little force with a screwdriver.
Most people do the opposite, tighten the risers by hand and the screws with a screwdriver, so no wonder they come of with the risers attached.