A semi-regular opponent bought the second version and asked if I'd like to play on an indoor hardcourt and see how well it would work. He had previously used it on a hartru court in a bubble, and said that he really had to clean the lines for it to register correctly. On the hardcourt it didn't take long to register, and during warmup I didn't notice any errors. But during the match there were a few serves that it called out that were clearly in, I mean within the service line, not on the line or back of the line. Those were on both ends of the court, but always on the service box farthest from the device.
It also called a few shots out that we both saw as in, but they were mostly in the corners farthest from the device. In one case he hit a shot down the line that landed halfway between the service line and baseline, and a good 6 inches inside the line that the device called out. Again, it was on the side opposite of the device. And there were a few instances of balls that were definitely out that it didn't call.
Even though he had been charging it prior to the match, it must not have been fully charged, because it only lasted about an hour. I don't know the level of charge prior to the match, and I don't know if the fact he was recording the match made it drain the battery quicker. I haven't heard back from him yet to see if the recording and stats were retained with the power loss.
He is planning on buying the baseline sensors, and may end up buying a second in/out. To me, as it works currently, you'd need to have a main unit on each side, and baseline sensors, and even then it would be like buying a good drone for personal use - interesting, but more of a fun toy than a tool. Maybe the recording and stats would be worthwhile for some, but not for me.
If it were more accurate, it might be a good purchase for our club, but they'd have to run power to the courts to keep them from needing to be charged, and do it in a way that didn't result in any cords on the court, so that would be extra expense, probably much more than the cost of the devices and baseline sensors.