5α-Reductase inhibitors like finasteride and dutasteride can slightly increase circulating levels of testosterone by inhibiting its metabolism .  However, these drugs do this via prevention of the conversion of testosterone into its more potent metabolite dihydrotestosterone (DHT), and this results in dramatically reduced circulating levels of DHT (which circulates at much lower relative concentrations).   In addition, local levels of DHT in so-called androgenic (5α-reductase-expressing) tissues are also markedly reduced,   and this can have a strong impact on certain effects of testosterone.   For instance, growth of body and facial hair and penile growth induced by testosterone may be inhibited by 5α-reductase inhibitors, and this could be considered undesirable in the context of, for instance, puberty induction .   On the other hand, 5α-reductase inhibitors may prevent or reduce adverse androgenic side effects of testosterone like scalp hair loss , oily skin , acne , and seborrhea .  In addition to the prevention of testosterone conversion into DHT, 5α-reductase inhibitors also prevent the formation of neurosteroids like 3α-androstanediol from testosterone, and this may have neuropsychiatric consequences in some men. 
It does work, however, I get pimples starting at about 3 weeks in to the regime. Could be because I am still a young lad. Who knows. I would not say they make the world of difference, but for me it is worth it. I would for you however, suggest just getting in shape first. (No offence intended) Get your training AND nutrition dialed if you feel you want that small edge, go for it. I personally just returned to the gym about few months ago. I waited until most of my initial strength gains slowed, and I also waited until I dropped a bunch of body fat. At high levels of BF, you will be seeing lower testosterone anyway… Why not get in shape first and maximize the benefits of all your training and nutrition
Spinach contains Magnesium which has been proven to be super effective at boosting t levels. In one study , researchers recorded the levels of testosterone and magnesium in 399 men with an average age of 74 years. They found that higher serum magnesium levels correlated positively with higher magnesium level and this was consistent across all the men. In another study, two groups of athletes were separated, and one of the groups was give magnesium supplements daily for 4 weeks while the other group was used as a control. The results showed a marked difference between the two groups with the group given Magnesium recording significantly higher free testosterone levels. However, it should be noted that both groups saw increases in testosterone due to the fact that they were both exercising a lot during that time frame. This reinforces the idea that foods like spinach combined with a lot of hard exercise will be a lethal combination in raising free testosterone levels.