Injectable steroids are injected into muscle tissue, not into the veins. They are slowly released from the muscles into the rest of the body, and may be detectable for months after last use. Injectable steroids can be oil-based or water-based. Injectable anabolic steroids which are oil-based have longer half-life than water-based steroids. Both steroid types have much longer half-lives than oral anabolic steroids. And this is proving to be a drawback for injectables as they have high probability of being detected in drug screening since their clearance times tend to be longer than orals. Athletes resolve this problem by using injectable testosterone early in the cycle then switch to orals when approaching the end of the cycle and drug testing is imminent.
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.