There is no pharmacopeial monograph, no standardized dose, and no regulatory floor on quality, so price tracks form factor, advertised purity, and how much active material is in the package
Journal of Orthopaedic Research , 28(9), 1155-1161
A very fine needle delivers the B12 into a large muscle, usually the upper arm, and most people feel only a quick pinch
otherwise GLOW covers the same regenerative components
none of the compounds have been studied for continuous use
Most users do well with 6mm needles, which penetrate deep enough to reach subcutaneous fat but not so deep as to risk intramuscular injection in typical sites