Well, you can't really feel it, I didn't anyway.
I have not had my T tested since I started, only my electrolytes. I think on Spiro alone you still have a high level of T floating in your blood anyway, you are still making it, so I'm not sure if the test would tell you anything. It is more that the spiro competes with it at the receptors.
Because you have more unused T in your system, you get more converting to estrogen, and this is where some of the effects come from.
Also the physical results of that low testosterone uptake and increased estrogen level can take a long time to manifest. We are talking numbers of months here.
That is my understanding of it anyway. Have a squiz at my blog - I have a log of the effects of hormones on me. For the first 3 months or so I only had spiro and results from that.
It is only now that I am on E that the endo said this will affect my testosterone levels. Sounds like it is actually estrogen which reduces your testosterone, not spiro. Spiro just sort of stops testosterone from affecting your body. (I could be wrong here....welcome any comments on this)