It's not that straightforward. I work in that domain and the general consensus is that the 787 system is about as efficient as a conventional bleed system would

It's not that straightforward. I work in that domain and the general consensus is that the 787 system is about as efficient as a conventional bleed system would be. It doesn't offer any significant efficiency advantage. The mechanical power offtake affects the engine fuel consumption less than the equivalent bleed offtake, but on the other hand their system is significantly heavier, and creates a lot more drag. Basically, the engine compressor is the best compressor you will find aboard. To provide air supply you need pressurized air. So it makes sense to directly take the compressed air you already have with that excellent compressor. With their bleedless system they add 2 large extra electrical compressors, and 2 large extra air intakes (to take the air to be compressed). So of course there are advantages to the electrical route, but efficiency isn't a given.