Testosterone and Tadalafil are helpful for different things. For example, testosterone will typically worsen BPH symptoms, while Tadalafil will markedly improve them. And obviously Tadalafil will improve erections, while Testosterone may or may not. Typically the cause of ED in older men is atherosclerosis of the arteries supplying the penis, causing reduced blood flow. Tadalafil improves the blood flow and alleviates the ED. Testosterone does not do this. However, less frequently, ED is related to low libido and associated sexual dysfunction, rather than specifically an problem with blood supply. In these cases, testosterone can help ED, but again this is a much less common cause and therefore testosterone is much less reliable as a treatment for ED. Effects on body composition, fat mass, muscle mass, etc. will be improved with Testosterone and not necessarily with Tadalafil. So to an extent it is apples and oranges, and it depends on what you need to treat, what your underlying medical condition is, etc.
Having said all that, the possibility of broader benefits from daily tadalafil is exciting, though unproven. It has been proven to improve ED and BPH. It has not been proven, despite some preliminary evidence, to reduce risk of cardiovascular disease and dementia/Alzheimers. However, this evidence is tentative because it is simply correlations found in the epidemiological data, and these correlations most of the time don't pan out to be causation. For example, imagine if you looked at a large sample of men that happened to be taking daily tadalafil for ED or BPH, and found that statistically those men had less heart attacks or dementia compared to similar aged men who don't take tadalafil. It doesn't take much thinking to realize that these two groups are not very similar. Men with a lot of chronic health problems, such as pre-existing heart disease, obesity, Diabetes, cancer, etc. are much less likely to be taking daily tadalafil then healthy men of a similar age. The really sick guys are probably not having sex. And they are more likely to die or have Alzheimers. It may just be a confounder. Until randomized trials are preformed, we won't know whether the purported broader benefits to daily tadalafil are real or not. And since it is generic, the funding for large randomized trials will be limited, so it is not clear we will get an answer.
