The Horizon scale needs a 500g weight for calibration. I have only used mine once when I first received my scale since it arrived in a slightly crushed box. I recall mine was off about 0.03g. In reality if your mix is off a few 100ths of a gram, you will not notice. one drop of VG from a 14g needle is ~0.03 grams.If you are weighing diamonds that would be significant, mixing juice, not so much. Up to you if you want to buy the weight. Mixing juice is really less about accuracy and more about repeat-ability, ie. when you make a mix that you like, being able to repeat the mix.
One item not mentioned are labels. You will need labels to identify tobacco, date, extraction method, etc..
Tip: The printing (markings) on syringes wears off very quickly. You can seal the syringe by wrapping in clear packing tape.