Hyperbole, any mirror organisms we cook up will be simple and inefficient since they won't be able to make easy use of the abundance of material that is the wrong chirality for their biochemistry. If they escaped they'd starve to death because all the normal life would be scavenging all the food sources much more effectively.
Its main advantage would be evading detection. However, this would work both ways. It wouldn't have the machinery to use 'normal organic molecules.
The 2nd issue would be its structure. It would be entirely synthetic. It will likely be trimmed down genetically. This gives it far less to work with in evolutionary terms.
Basically, it would be a shadow environment. It would be dependent on whatever material it could find, since no current life would be producing what it needs. It would also be limited in it's ability to evolve rapidly to cope.
It would be akin to releasing a pregnant chiwawa into an automated car factory. Could it survive, maybe. Could it cause a bit of damage, maybe. Could it multiply out of control, consuming the machines of the factory, VERY unlikely.