They’re mostly only reliable for raws and orals, and orals you have to be careful too. Carrier oils unfortunately change results for injectables. For orals, things get wonky with fillers as well. Frequently you’ll see oxandrolone tests that look “too brown/green” to test as pure, but with the variety of fillers people use, it’s hard to differentiate between the brown of the whey filler, for example, or the deep olive that stanozolol will produce in a var test.
They’re fairly reliable for qualitative testing of raws, in my opinion.