Can I just use a regular syringe with mL markings instead of an insulin syringe? Would that be easier?

You can, but I wouldn't recommend it. Standard syringes typically come in 1mL, 3mL, 5mL sizes with much coarser graduation marks. A 3mL syringe might only have markings every 0.1mL, which means you can't accurately measure the 0.05mL or 0.068mL volumes that some doses require.

Insulin syringes have two big advantages: (1) finer gradations for accurate small-volume measurement, and (2) shorter, thinner needles (typically 29–31 gauge, 8mm or 12.7mm) which are ideal for subcutaneous injection and much more comfortable.

Just remember: 100 units = 1mL. Engrave it in your brain and the rest is just arithmetic. 😄

Got it. 100 units = 1 mL. Syringe "units" are just volume. Concentration bridges volume to mg. The engineer in me is finally at peace. Thanks everyone.