I use an Apogee MQ-500 and have tested both Photone and the Uni-T light meter.
After tested Photone and, after trading "programmer to programmer", I would recommend growers not use a phone + an app, especially on Android.
Photo BIO - no thanks. Per the Apogee website, the sensor that's used in the OEM sensor that Photo BIO repackages cannot read light levels if light wavelength > 660nm. That's OK for up to red but it does not respond to photons that are in the far red and high parts of the spectrum. In addition to documenting that limitation of the sensor, Apogee also documents the inaccuracy of the sensor. Check out their white paper for additional info.
I don't know much about the Spot On. It's $400 and it's got a wand which, in some situations, is very helpful.
Having tithed to Apogee to the tune of $600, I'd argue that most personal growers are a lot better off spending $35 on a Uni-T than they are spending $$ on an Apogee. The Apogee is a superb instrument but the law of diminishing returns kicks in really hard…at about $36.
I don't specify Uni-T over any other lux meter for reasons other than it's very popular, it's cheap, and I've tested it against my Apogee (Chilled X2 veg light, Chilled X3 flower light, Vipar XS-1500, and Mars SP 3000). A grower using a conversion factor of 0.015 or 0.016, will get results that are,
in practical terms, the same they I get from my $600 Apogee set up.
In short, if you need a wand to take measurements or if you're spending someone else's money and want to CYA, I'd go with the Apogee ePAR sensor. Other than that, a Uni-T for $35 will do just fine.