I feed homemade raw, and I have done a huge amount of research on it, but I use Alnutrin supplements and am not familiar with EZComplete. I've taken a quick look. It includes liver and pancreas and a calcium additive and so clearly is made to be used with muscle meat only (presumably it is designed to take care of the 10% organ and 10% bone; you supply the 80% muscle meat). However, it doesn't specify the type of meat, so I'm not sure how they can know they have the Ca: Ph ratio correct - probably they assume you'll use chicken or turkey for a cat and it will be close enough.
No, no assumptions are made. Actually, the amount of phosphorus in meats doesn't vary enough to need to pinpoint the amount of calcium used to balance foods. As you've pointed out, the prey model raw diet is 80% meat, 5% liver, 5% other secreting organ, and 10% bone. Well - that's for dogs. Cats usually need less bone (dogs have a higher calcium requirement), and PMR for cats is usually 82% - 83% meat and 7-8% bone. Plenty do fine on 10%, but many develop constipation at that level. The amount of bone doesn't vary dependent on which meat is being fed. When using an appropriate amount of fresh bone alternative, in this case eggshell, there's no need to use an exact amount depending on which meat is used. Yes, Alnutrin has a calculator on the site so you can do that if you want to, but the instructions on the bag are to use the measuring scoop that comes with it. There isn't a different scoop for each protein.
When I first transitioned to raw, I quickly learned that my cats preferred eating chunks. Yet many were seniors when we transitioned, and they weren't chomping bone (some still don't). So I needed an alternative. What I learned is published in an article on whole bone alternatives in the raw diet, hosted on Catcentric, here:
http://catcentric.org/nutrition-and...n-and-how-to-use-them-in-a-raw-fed-cats-diet/
As you can see from the tables in that article, when balancing the phosphorus in muscle meats, the amount of calcium needed isn't sufficiently different to need to fine tune how much eggshell (or any whole bone alternative) is used. With 1/2 teaspoon of eggshell per pound, the calcium: phosphorus ratio will almost always fall within the AAFCO defined 1.0:1 to 1.5:1 ratio. Of course, cats actually do best at 1.3:1 to 1.0:1, anything higher tends to be a bit much calcium for them. But actually, as with any diet, especially raw or cooked, we encourage people to use both a variety of proteins and cuts of those proteins - ensuring that one isn't using just one meat that will result in a higher or lower Ca: P atio.
In fact, we have analyses up on the site: with the turkey breast we sent to the lab ( turkey breast + EZcomplete) and the Ca: P ratio is 1.3:1. If one has turkey breast, chicken thigh, and pork loin in rotation, the Ca: P will be 1.2:1. If one has rabbit, venison, and pork in rotation, the Ca: P will be 1.2:1. We didn't publish all possible meats and diet possibilities, but chicken, depending on cut, is 1.2:1 or 1.3:1; beef is 1.3:1, turkey thigh is 1.4:1, breast is 1.2:1 - so as you can see, with a healthy rotation, it will average out to 1.2:1 or 1.3:1. But you can take a look at the tables in the article linked to above. And please don't feed only gizzards.
Oh - edited to add the link to the analyses, hosted on our website:
http://www.foodfurlife.com/ezcomplete-fur-cats---chicken-liver---analysis.html
Overall the ingredients seem sound, and it contains nothing I'd object to for a cat, unlike some of the raw-food supplements I've seen. But that's just a rough first impression, not personal experience. You might try asking in the raw feeding forum on The Cat Site:
http://www.thecatsite.com/f/65/raw-home-cooked-cat-food
Interestingly, I learned about raw feeding on forums of TheCatsite, and how to use eggshell in a modified prey model raw diet is information that evolved in discussions on TheCatSite! I joined in 2002 when it was less than a year old and have over 40,000 posts there. I am user LDG. I actually created their raw AND cooked feeding resource posts (sticked at the top of the forum - you can only see them if you're on a laptop/desktop, or in desktop mode on your mobile), and wrote many of their nutrition articles and the entire series on raw feeding, hosted in the Healthcare section within Articles, along the top tabs.

So yes, I'd have to agree, the forums of TheCatSite is a great resource.