Quest Engines Same as Estes?

From a recent post on TRF:
"Quest motors are interchangeable with Estes motors --- they are the same size and basically the same construction and the same propellant. They are close to the same price. 
So if you have a rocket that can fly on Estes A, B, C motors, it's going to fly pretty much the same on a Quest A, B, C motor."

My response:
Sorry, I have to disagree.
Personally, wouldn't use a Quest C6-5 in a tall BT-60 sized model.
Say for instance, the Quest Stiletto.
The model could be too heavy to stay in the air under the lower sustained thrust.
Initial peak thrust is good, then look at the low sustained thrust.
There is also too much area for the (weaker than Estes) ejection charge to pressurize.
In minimum and smaller diameter models a Quest C6 (Chinese made) engine is fine.

Depending on the lot, Chinese made Quest engines can be 3/32" shorter than an Estes. 
The engine could slide forward during boost and back at ejection.
3/32" is a small amount but might wear at an engine hook slit.
The thinner casings get hot and could melt a plastic fin can or retention ring.
Quest engines are different and should be used in appropriate models.

One problem and more confusion - there are plenty of German made (Quest re-labeled) engines out there.
The German made engines had silver nozzles.
The Chinese made engines have tan nozzles. 

This is not meant to bash the Quest engines.
I like the Quest A6-4 and B6-4 engines and use them all the time.
They are loud and sooty, but that easily cleans up with a damp paper towel.
I just bought 125 more of them!