Enviro-safe, hmmmm . . . interesting website. Well, it's endorsed by GreenPeace so it must be good, right? And it smells like pine . . . for leak detection they say. Ah heck, I say put it in and see how well it works.
The PittStop oil testers look like they should be sold by Billy Mays.
You can use those if you like, but your taking a chance with your new compressor and from the sounds of it, it might already be suffering. If you really want to be on the safe side and not risk your compressor - do as suggested - flush your system, vacuum down, replace dryer, and then recharge with oil. Otherwise you just don't know and you'll be singing the blues with a bum compressor. On the up side, your bum compressor will smell like pine.