Not sure what is meant by protected and unprotected coils. I use both SI and kanger branded horizontal coil 808 cartos and find them to be pretty much the same, inside, out, and performance wise. Thats why I go for the kangers that I can get at under $5 a box.
The SI's are excellent cartos, but so are the kangers. There are subtle differences in appearance, I can tell a SI because the connector pin at the battery end is slightly wider than on the kanger, also the condoms are different, otherwise these cartos seem identical.
The coils in both have the split centre tube covering them. Is this what is meant by protected?
Are you sure 'protected' isn't vendor hype?