I had been using the same PI EMS-PT50C for almost 7 years until September 2016 when a lightning strike in the park I was in apparently sent a surge to me and one leg of the PT50C died (no damage to my rig or any electronics). It was the original design with the open socket and never an issue. It was sent to PI for warranty and they replaced it with the new design with the lexan cover that flips down over the socket. I also had a spare PT50C also with the open socket which was put in service in September 2016 when the above lightning strike occurred and this past March I was in a major thunderstorm with 50-60 mph winds and horizontal rain. The PT50C would not work after this storm passed. My spare was put in service while the dead unit was sent back for warranty. It too was replaced with the new lexan covered design. This was the first issue I had with the open socket design in almost 7 years full time service, but then this was a major thunderstorm.
My hat is always off to PI and their EMS products. I will never plug in anywhere without my PT50 in line.