Pros of Testosterone Injections:

Injectable testosterone is inexpensive if self-administered. The two most common forms (testosterone enanthate and testosterone cypionate) are both generic medications in the United States.
Only need testosterone injections every two weeks (for testosterone cypionate and testosterone enanthate). A longer lasting version, testosterone undecanoate, is now available in the US. The FDA approved injectable testosterone undecanoate in 2014. Endo Pharmaceuticals will market it under the brand name Aveed. It will extend the period between injections to 10 weeks after an initial ramp-up period.
Flexible dosing. Dosages can be changed with each injection, if necessary, to achieve optimal concentrations.

Cons of Testosterone Injections:

T levels fluctuate between TE and TC testosterone injections. This results in more negative side effects than administration methods that provide more stable blood testosterone concentrations. Shortening the interval between injections and lowering the dosage proportionally can minimize this cyclical nature of highs and lows. The longer lasting version of injectable testosterone, testosterone undecanoate, maintains T levels in normal ranges.
Testosterone injections are more likely to cause an increased red blood cell count than other forms.
Injection site pain is relatively common.
Need to visit a physician for testosterone injections if unable to self-administer at home.

Suppliers

Both testosterone enanthate and testosterone cypionate are widely available in generic forms. Testosterone undecanoate is marketed under the brand name Aveed by Endo Pharmaceuticals.

Injection Information

For injection information, the University of Michigan provides a detailed primer on How to give a Testosterone Intramuscular (IM) Injection. Also, ask your physician to explain and demonstrate the technique.