The special binder is Butcher & Packer #414 (a phosphate binder for sausage), AmesPhos is another popular brand but I think it is being discontinued. Phosphates help with the retention of moisture in sausages. I think it also makes the mouth texture better (smoother). Pretty much all commercial sausages will have a phosphate binder, but by letting the commercial butcher keep more mositure/water in the mix it is also a cost effective additive for commercial purposes (basically you are paying for more the liquid it holds instead of more meat, but it does improve the meat quality). you can see what I mean about the appearance of the texture in the close up photo I took of the cut sticks in the first post in this thread. I think the proper application of phosphates improves the product quality (but you can over use phosphates from what I have been told - I have not done so yet).
ECA is encapsulated citric acid. This is a way to get the twang you get from real slim jims and other fermented sticks without having to go through the multi-day fermentation process. Basically little balls of citric acid are encapsulated by a outer shell of fat. The fat will melt in the 140-150* range during the smoking/cooking process and release the CA to do it's thing. By then the meat is set and you get just the twang. If you put powdered CA in instead of encapsulated CA, it starts to work while the meat is still raw which will turn the color whitish/grey and also make the texture grainy. This will also happen if you add the ECA in advance and let the mix sit or add ECA with a grinder as the stuffer. ECA should always be added by hand mixing at the last minute before using a manual stuffer. That way the meat will set before the ECA is released. Some people use cultured buttermilk powder (Saco buttermilk from the grocery store baking items isle). It will also add a twang, but the ECA is more pronounced IMO and I like it better. Also a little goes a long way as I only needed 17 grams for a 5 pound stick recipe. I have gotten to the point that I use ECA in probably 90% of my sticks. I will try a new mix "as is" first for the other 10%. I bought some Owens BBQ mixes over the holiday and will make at least one batch of each flavor "as is" from the directions first.
And yes, AC Legg mixes like the #116 do come with a bag of cure (unless it is a fresh sausage mix). The cure is in a separate bag and not pre-mixed with the other spices. This also lets you take a bag of mix that can make 25 pounds and measure out enough for whatever weight you want to make. I usually run either 5 or 10 pound batches. I just had some LEM cure that was already open and saved the Legg cure packet for later, using the last of my LEM stock. I have not tried the 188 mix, but I do often add jalapeno powder to my sticks & sausages. I'm a fan of that rather than using cayenne as you get more flavor and the heat is not just pure heat like it is with cayenne. It has character. I have a Savor Spice Shop near my office and I get my jalapeno powder and 4 kinds of very wonderful and fresh paprika from them now. If you have one near you, that place is a sausage maker's spice heaven. They have dang near every spice I would ever want and the quality is spot on IMO.
Bottom line is don't be afraid to doctor up a store bought spice mix (but try at least one batch as in the directions). Also keep notes of what you changed/added and how it came out. Nothing like 3 months later thinking those sticks I doctored up a while back were pretty good, now what was it I did and how many grams those extra spices did I use.....