Both B12 and glycine are optional additives you can include with your prescription. Neither changes how the active ingredient in your medication works.
B12: B12 is a vitamin commonly associated with energy and metabolism support. It may be a good fit if you're concerned about fatigue or want extra energy support while on treatment.
Glycine: Glycine is an amino acid commonly associated with muscle maintenance, which can be relevant since some weight loss includes lean muscle along with fat. For some patients, it may also help ease certain GI side effects.
There's no wrong choice here. It comes down to which benefit matters more to you: energy support with B12, or muscle and GI support with glycine.
If you're not sure which fits your situation, you can ask your clinician for their input, and you can typically switch additives on future orders if you change your mind.