We are using Bonita BPM to a small extent, because we are small organisation. Bonita BPM is used mainly for supporting contracts management. Our experience is built on deploying the platform to our clients.
It is a very low cost platform. You can start with open-source edition which is free and with the application number growth upgrade to subscription editions for more features and support. Subscription editions are still not expensive compared to bigger players platforms.
It offers a great UI designer tool for rapid building process forms and web applications.
It gives a lot of flexibility and extensibility. It comes with features like built-in connectors, convenient API, and a web portal. You can add your own connectors, extend the API and customize the portal for your own needs.
I found Bonita BPM a more friendly environment, especially when it comes to front-end development. It is also better suited for a gradual introduction to an organization - PoC with Community edition, later upgrade to one of the subscription editions as needed. Tibco's product has partial case management support and stateful tasks, though.
Bonita BPM has an efficient engine which can be tuned and clustered. Although I came across a case when the engine did not manage to handle a great number of event handlers and the process required redesign.
Engine itself is efficient enough for most cases I dealt with. It can also be extended by clustering. I have done performance tests with JMeter and only managed to induce the crash of... JMeter. If there are efficiency issues they usually concern bad design/implementation of created apps or bottlenecks in integrated systems. Although I have met two cases with efficiency loss.
1. Java 7 related PermGen saturation caused by big number of installed apps (there is no jar dependency reusal between apps option).
2. Big number of waiting event handlers in processes stresses the database.