Mr. Finnan,
Are you sending the signal down one (or both) of the lines?
If not, I see an opportunity for minor improvement, or maybe two product lines based on pilot's choice.
I suggest making your control module as a wearable unit by getting it out of the handle.
It is not uncommon that model airplane pilots dedicate one handle and lines per plane. This minimizes any changes to any part of the control line system for each model. A wearable module can be moved/ bound to each airplane as wanted/required without disrupting a matched plane/lines/handle set.
While having the throttle on the handle may be particularly convenient for single hand operation, any other feature requiring a second hand will require two steady hands on the controller/handle ("stick"). Make the module so it could clip onto the operator's belt for easy operation of the other features and throttle with the free hand. This segregates "features" remote control actuation from negatively influencing the "stick," This isolation prevents any undesired movement or restriction of the handle. The controls can then be made a bit bigger and easier to manage by the "non-flying" hand. I'd rather have the throttle packaged with other controls off-stick, so that my single-handed "stick" remains a single-handed stick, rather than trying to operate the stick and additional controls with two hands during any phase of flight...especially when the lines go slack. In short, there just isn't any good time for two hands on the stick.
Your handle with battery and controls will be heavier than a common control handle with respect to model scale. The difference gets smaller as the planes/handle get larger. This is particularly important for 1/2A where the airplane could be as light as only several ounces. As.an example, my own 1/2A control handle is just over an ounce yet sufficiently strong.
It is important that the control handle is as strong as possible, maintaining adequate strength for line yanks such as when the lines go slack, and the plane snaps the slack out. Additionally, my safety cord/thong goes through my handle where neither the handle nor thong will fail should I inadvertently let go of the handle. I am concerned that your small thong "ringtab" lacks strength and durability, especially on heavier/larger scale jobs.
While I do like the idea of throttle and retracts, I'm also cheap and build small. If I ever build a four foot twin with throttle, retracts and elevator-coupled flaps that could be uncoupled from the elevator for landing, I'd be looking for an "off-stick" control system such as I described above.
I wish you the best in your endeavors.