Yeah, that is what I had heard about that plugin - it’s extremely inefficient.
Regarding Montage ESP plugin - I bought it two months ago, from a friend who purchased Montage M synth, but does not use any of the studio stuff.
It is far optimized, uses only one cpu core, and is highly dependant on the cpu clock - on cpus under 3.5 ghz it is almost non-usable.
I am building two hardware workstations, and in them are much stronger processors with clocks above 4.5 ghz - they both handle ESP without problem.
Still didnt have time to explore complete midi mapping, but for know I did map super knob and parts levels - still didnt have time to figure out how to change scenes, which I use a lot with my Gen 1 montage.
What I noticed is it does not react to variation changes - so count on that. Every change to happen, even within same performance in ESP, it has to be in separate rackspace.