On a side note, recent experiments have shown that electronic x-tail mixers and levellers can sometimes react in strange ways.
My recent experiments with a GWS V-tail mixer and one of my levellers showed that under certain circumstances, the servo movements can become 'bitty' or 'grainy'. I think this may be something to do with pulse timing, both units are using microcontrollers to modify the incoming pulse from the receiver, but it's an interesting phenomenon.
Norbert Bruggen now sells a small leveller designed purposely for x-tail submarines, as it has a built in mixer. Seems elegant and straightforward.
More information here.
(scroll to bottom of page- in German only I'm afraid)