Have you ever compared it to the Photone app? Maybe help them gauge their parameters. I got lucky and low ran his expensive par meter with the same light setup and now I can be in ballpark.
This is how I know my 1,000 ppfd reading was just through the roof. I only had 2 100 watt spider farmsf1000 in a daisy chain so 200 watts. Earlier I had mentioned low doing a rough estimate for me
Prior was showing me the readings with his lights and I believe the Photone app was off around 100 ppfd.