Testsosterone implants contain 800 mg of testosterone (usually in the form of four 200 mg pellets). They are implanted into the buttocks or abdomen, and provide testosterone replacement for around six months. Implants are replaced periodically, once symptoms of testosterone deficiency recur. Inserting the testosterone pellets is a minor surgical procedure, requiring local anaesthetic ; this is the major limitation of this method of treatment. However, men using this form of testosterone replacement are usually satisfied with the method, and are more likely to continue being treated than men using other modes of testosterone replacement.
I think this approach is fine. I must say having been doing this for years, treating hundreds and thousands of men I have been underwhelmed with the results with topicals. Injections can cause peaks and valley and I have many younger men inject twice a week that smooths out the peaks and valleys. I think it is appropriate to follow the advice of your primary doctor and endocrinologist. I have just seen too many men spend months or years with gels with sub optimal results. Many men are diagnosed with depression and are not really depressed (I have no idea if this applies to you), but the presumed depression is base dupon low T.
My recommendation would be to pursue this but if a few months pass and results are modest consider another approach. Pellets are one approach to have smooth levels of T and are placed every 4 months.