Many people use a combo of Metabisulfite powder and citric acid as a sanitizer for winemaking. This is a pretty age-old practice, and for the most part is fine. Here at MoreWine! we recommend the use of StarSan for a couple of reasons, but ultimately the decision - as always - rests with you.
We avoid using Metabislufite as a sanitizer because the 10% solution of sulfite that is generally recommended for sanitizing is about 2000x the usual concentration of sulfite in your wine. Most texts recommend rinsing this solution off of the equipment that you have just sanitized, but as you can imagine unless you are using pre-boiled water for this rinse you are really just re-introducing bacteria to a surface that you just took the time to clean. Not rinsing the solution off of the equipment will lead to very high sulfite levels in your must or wine, which can lead to fermentation and ML problems as well as impart an off flavor to your wine. Additionally, strong sulfite solutions are a bit rough on the skin and lungs. Finally, citric acid - which is used to increase the effectiveness of the Metabisulfite powder - is a direct precursor to acetic acid and if not removed can help lead to the vinegaring of a wine. So we try to keep citric out of the winery as well.
We use StarSan
as our general use sanitizer because it is a safe, easy alternative that carries no risks. StarSan can be used to sanitize all of your equipment, as well as yourself, with no risk to your health or the health of the wine. Also, it does not need to be rinsed off. So that's our $0.02, but like everything else in winemaking there's no 100% right answer - so do what feels right to you.