What are the limitation flowable engine has with Mongo DB and shared mongodb cluster

What are the limitation flowable engine has with Mongo DB and shared mongodb cluster

Please share your suggestion , i could not find anything related with mongo db support and limitation .

when i search for limitation i could see below comment
This repository contains the source code for using MongoDB as a persistent data store for the Flowable process engine (support for the other engines (CMMN/DMN) are not yet implemented). It is currently considered in alpha state as not all features have been implemented.

Thanks.