I haven't had tests taken regarding my testosterone and ROP usage, but if nothing else it can work as an all day cockring of somesort.
You can build the unit by yourself, getting the parts for it can take some effort. I actually ordered the zinc rod from a welding company, which was a bit strange but worked out in the end. Copper piping I had laying around.
One could do a built where the copper is a rod as well, but that would add more weight to the unit.
For the "connection" I have used silicone tubing. It's most suitable for many skintypes and very safe on your skin. It's best to buy some excess tubing as the oxidiation will happen and if you have clear tubing, it will show! Nothing wrong with it though, mainly it kind of tells that there is something going on!
Anyhow, as said, no tests done but I don't have anything bad to say about the ROP. In a way if you make it yourself I think your mindset can be more immersed in the whole PE "game" and can in that way speed up your progress!
http://www.mattersofsize.com/forum/alternative-and-experimental-penis-enlargement/3101-the-ring-of-power-49.html#post542161
There's the link to my post where I show the one I made, long time ago. Just to combat with the unit falling off; if you use long enough string you could loop it to your pants! It's annoying feeling if the unit comes off. Using just tubing that was an issue for me, with the string method it was much better!
If possible, make it yourself. I think you can get the supplies for several rings for under 20 USD. Might take some time looking though, remember to get highest purity zinc rods you can! With copper the selection is easier.
And it's best to buy some scrub pads for cleaning the ROP.