You guessed audio-feature difference right.
We are in process of creating a page to provide a comparison table for all 3 video-solutions we provide (there is third, video-encoding as service feature we provide here - http://rtcamp.com/rtmedia/addons/audio-video-encoding-service/ )
Sticking to FFMPEG v/s Kaltura Addons:
We do not have any feature is pipeline to be added to Kaltura Addon. It is mostly for users who uses kaltura already or like kaltura for their player/analytics/reports etc feature.
In case of FFMPEG, all we are doing is raw audio/video encoding. For job-queue, we are using node.js - http://github.com/rtCamp/media-node
FFMPEG-addon for sure is more CPU/resource friendly. It doesn’t have any analytic/reporting feature (we assume wordpress sites already use Google Analytics, JetPack stats or some other analytics so no need to add analytics again in video backend).
We will be adding more features to media-node as we use it for our audio/video encoding service. Some of these feature will be available for FFMPEG users.
A key difference is FFMPEG-addon requires VPS/Dedicated server so you can install media-node. For Kaltura-addon you can use kaltura.com or kaltura-on-prem account to skip installing Kaltura-CE.
But again if VPS/dedicated is a reason for going with Kaltura.com, then http://rtcamp.com/rtmedia/addons/audio-video-encoding-service/ is a nice alternative.
Rest assured both addons are developed by us and bug fixes (if any) will be covered for free by our promise - http://rtcamp.com/promise
Though we cannot guarantee future of Kaltura-CE server. They have history of NOT giving upgrade scripts when they go for major releases. That is only reason that we choose to create our own media-node!
If you have any more questions or need any details, feel free to ask.