Gold contact finish is standard here, suited for signal-level currents and repeated mating cycles without corrosion issues. Solder retention features on the SMT pads help keep the connector anchored during reflow and under any incidental cable or board strain.
At 0.50mm pitch, the footprint is dense — routing all 50 traces out from under the connector demands either fine-line PCB capability or a fanout layer change. The 4.5mm mated stack height is a mid-range gap; it gives room for passives on the underside of the top board without bumping into the bottom board.