Let me see if I have this right because this is a tad confusing.
The various curing salts labeled as #1 (InstaCure #1, Prague Powder #1, etc) are a mixture of Sodium Nitrite 6.25% and Sodium Chloride 93.75%
The various curing salts labeled as #2 (InstaCure #2, Prague Powder #2, etc) are a mixture of Sodium Nitrite 6.25%, Sodium Nitrate 1% and Sodium Chloride 92.75%
Morton's Tender Quick would seem to be a #2 type curing salt but that is not clear from the packaging.
As far as use goes, it would seem that the #1 curing salts are used in short term storage preparations such as bacon, guanciale, etc. while #2 curing salts are used for long term storage preparations such as dried sausages, prosciutto, etc.
The main difference between #1 and #2 curing salts being the addition of nitrate to the #2 salt.
I've read the threads about saltiness degree, and how one cannot be substituted for the other, etc. and I can see the merit in every opinion. In the end though, it seems to be more about how salty the final product is rather than effectiveness. I like the "fry test" solution - why guess when you can taste?
I'm new back into smoking and there have been many changes. When I did my first hams and fish, curing salt choices were not an option. We used pharmaceutical grade saltpeter (nitrate) and mixed our own percentages.
Looking forward to starting some belly for bacon this weekend along with some hocks. Got fat t render and cure and perhaps come confit to make from the trotters. Fun stuff!