Use Only Centuri Engines?

Dannymrmissle scored a mint, bagged Centuri BATROCK kit 

and posted this picture on YORF.

Notice the bag topper line: "USE Centuri safety approved rocket engines ONLY with this rocket kit."

Why would it make a difference?

Most never knew that Estes made the engines for Centuri until the early 1970s. Here's an picture from the 1969 Centuri catalog:

Early on, I remember thinking: "These Centuri engines sure look a lot like the engines I get from Estes."

Then, the Centuri Phoenix made engines appeared in the 1970 catalog -

Those new rolled on graphics were slick!

We'd still find the older Penrose made engines with the Centuri name on them for a few years until the older stock was depleted.