I have successfully used one from this source:
https://www.instockwireless.com/gps-splitters.htm. I use one gps puck antenna for all gps-dependent devices without issues (Flarm, LX9000 and Mode S transponder. My IGC file submissions to WeGlide and OLC are consistently validated, but cannot speak to contest or record claims. ADS-B PAPR reports from FAA come back consistently clean, also. One thing I would caution is to use the best quality, factory recommended cables of appropriate length to each device, along with a quality antenna.