1000 mg b12 injection Out of Stock - VITAMIN (Generic) Injectable Solution, 1000-mcg/mL, 100-mL vial - Easy Refills What is Cyanocobalamin (Vitamin B12) Injection for Cats and Dogs Vitamin B12 Injection: Energy Boost
Description
NNMT uses up nicotinamide by tagging it with a methyl group (a process called methylation) and sending it out as waste

The honest answer is that they are not competing tools

(PubMed) Smith AD, Refsum H

Injections help prevent or reverse this

For a healthy person eating meat, dairy or fortified plant foods, the NHS view is that you do not need B12 injections