Another, it's my understanding that a TSO just states that equipment meets certain standards. It's up to a government agency to require that the equipment meet those standards. Not all GPS receivers meet any TSO, and it's quite legal to use those receivers for some things. I have a handheld backup that I carry, & often use on the ground. It meets no TSO, nor is it required to. I could use it for IFR flight, but the FAA forbids it. It's the FAA that requires the equipment to meet the TSO. If I'm in error on this, please point me to the correct documents.