Percents of machines?On a weapon of course
I would find it quite useful, do to the facts that machine type enemys
always beat me up

Because machines aren't a very diverse range of enemies, and don't appear very often outside of episode 2 & the mines in episode 1.
I like machine %, but on pso bb you can see that in ep4 and in ep2 you rarely find a machine enemy, even on ep1 you only need to worry about 1 area.