We use both Epic and Cerner.
James covered Epic well. Epic is not difficult to work with. I really love that we have direct access to an Epic EDI engineer for support. Bridges is a nice, straight forward set of tools to manage interfaces, but is not an engine.
With Cerner you must have their interface engine (OpenEngine or OE) installed and you can work in OE and connect point to point with other applications or, as we do, use Cloverleaf as a central hub.
You can have OE with or without a developers license. Without the developers license, you can configure comms, start/stop interfaces and change a few options — most everything else will require a Cerner paid engagement to change or add interfaces. MDI’s also run through OE.
OE is nowhere as straight forward to use a Cloverleaf as there are two different front end tools as well as an almost non-documented back end module for the Oracle side, and most of the coding is done in their proprietary SQL, Cerner Command Language (CCL).
Support is all on-line, a little convoluted and customer service generally assumes you have a developer’s license and commensurate training/experience to implement your own fixes.
Hope this helps.