Welcome to the forum, we recommend T-SPX because in our experience it does a good job at relatively low temps like 70F, which is normal room temperature available to most people in their home.
We don’t have any experience using Fermento. My understanding is that Fermento is not a starter culture but rather cultured whey protein powder which is recommended for semi-dry sausages like summer sausage, etc.
Fermento is probably used for fast acidification to simulate the tangy flavor of fermented sausage without having to actually ferment the sausage. This is probably not an appropriate product for dry sausage.
Starter culture is used to ensure that dry sausage ferments properly and the ph of the meat drops into the safe zone to protect against the growth of pathogens during the drying period. It also adds a complex tangy flavor traditional to most dry salami products.