Before we switched to Poly John we used Poly Portables, one of the reasons we switched to Poly John was that their restrooms looked very similar to our old Poly Portables so we could get away with using them both at one site.
What made us change our minds on using the Poly Standard was the extra price and that we got sick of changing springs. If there's one defining flaw it's the door spring, they're guaranteed to fail. Unfortunately they haven't really come up with a good solution to fix the problem. The real issue is regarding the cable at the end of the spring and the metal retainer at the end of the metal cable. It breaks because naturally the retainer is supposed to rotate to keep the spring/metal cable parallel to it, however it corrodes (aluminum?) and in a few months it doesn't move freely anymore, it simply pops several times when opening the door. After a couple of months of bending back and forth the metal cable snaps and the door won't stay shut anymore. TIP: to prevent further problems spray that area of the spring with oil or lube it makes the spring last many times longer.
Other issues are the vent pipe, it's brittle and commonly breaks, though this may be fixed by now. The vents around the roof seem to some how break apart also.
Another concern maybe the CEO of the company, she has been known to have a bit of an attitude and was quite rude to me a few years ago. The lack of professionalism and integrity is one of the reasons why I no longer do business with her company.
If buying used "Poly Standards" make sure you don't buy ones with wooden feet, they're quite horrible. The feet rot and come loose from the base of the toilet. They're also horribly heavy and hard to drag around. They updated first with a solid plastic skid that was a bit brittle (especially when you drill stake holes), to a hollow version with stake holes built in (the best type).
These restrooms make decent portable toilet trailer candidates, the tanks are made so they can stop some waste from coming out.
In Conclusion, these are pretty average toilets, they're an old design from the early to mid 90's, there's decent sign space and amenities for most of your customers.