I forgot to mention, the AE compatible version of Twixtor 5 does not work in FCP, only projects saved with the FxPlug version Twixtor 4.5 projects will work with Twixtor 5.0 Fxplug (native plugins supported by FCP). You might need to copy the setup.
Unfortunately for FCP users it’s highly probably that the next major release of FCP will stop supporting AE plugins (a bit like Motion already “forgot” to turn support for AE plugins on).
Pierre