I use a couple of lights whose model have been tested in a real Integrating Sphere (Like the Fenix L1P) and use that as a benchmark.
Of course, this is probably not accurate and as light output goes up, it seems that readings are more inaccurate (like blasting a Mag150w in the lightbox), but for lower end lights, it seems to be acceptable.
Ultimately, its for fun and its useful for comparative purposes among your own lights!
I have a PE-1. Only things that would make it better would be a backlight and a laser pointer. For the price I can't complain, I think I found it for under $20 on ebay.
I'm also looking for good places to buy soldering equipment. I only have a big old basic iron right now, which won't be good for the connections on emitters and drivers.