"such drugs have potentially serious adverse effects on the cardiovascular system, prostate, lipid metabolism, and insulin sensitivity." Not quite side-effect free.
I don't think anyone says that they are side-effect free. The emphasis here is on "potentially". The potential effects are known. The important question is how often they occur in actual usage, and how severe are they when they occur. It's assumed that the potential for significant harm would increase with longer periods of use, but again, this needs to be determined by actual experience.
"The absence of systemic toxicity during testosterone treatment was consistent with the results of studies of the contraceptive efficacy of that hormone."
This sentence has a reference to a study from 1988 on high-dose testosterone used over a period of 6 months in a small number of men as a male contraceptive. I can't access the full text of 1988 articles, and the abstract doesn't say what the actual dose was. But the authors of the Bahsin article imply that there were no significant SEs in that study.
Again, it would be nice to see large, longer duration studies of adverse effects.Here is a meta-analysis
of studies of benefits and risks of long-term testosterone replacement. All of these involved attempts to bring test levels up to normal, not the supra normal levels of the Bahsin study.