Instacure #1 and Prague Powder #1 are the same, containing sodium nitrite with table salt.
TenderQuick has sodium nitrite, sodium nitrate and table salt. Cure #2 also contains sodium nitrate.
Do not mix Prague Powder or Instacure with TenderQuick.
Cures are applied once at the start of the curing process, when using a dry-rub method. Wet-curing or brine-curing starts with a predetermined concentration in the solution, and this solution remains unchanged during the curing process, then is discarded when curing is complete.
Any cure #1 is suitable for faster curing of meats that will be fully cooked prior to consumption (bacon, ham, cured sausages). Cure #2 is suitable for slow curing or dry-cured fermented sausages. TenderQuick, technically, is suitable for slow or fast curing, but I fail to see the benefit in having a fast curing agent involved with a slow cure process...it may likely hinder what some processes are intended to accomplish with a slow cure. I've had good results with all of my fast cures done with TenderQuick.
Always follow the manufacturer's label recommendations for applications of ANY curing salts. Online info is available if you need their specific info, such as recommended concentrations for brine cures or amount to use per pound of meat for dry-rub cure methods, prior to buying.
Eric