nothing can beat the softness of squirrel hair! this is great in picking up pigment either matte or shimmers like Tom Ford eye quads (the wet and dry formula type). Using goat hair, I need to use MAC fix plus or urban decay all nighter for the shimmery eyeshadows to adhere on the brush. But with Z-5 one light tap on the Tom Ford shade (the topper/lightest shade) although you won't notice it on the brush but once laid down on the eyelid, one swipe and your are done. Being made from squirrel hair, it does not require harsh cleaning or it will be damaged. I can use this brush alone shifting from light colored to dark colored shades without any color transfer (just wipe it with micro fiber cloth when changing shades). So for me this is great, less time spent on washing and drying. But of course, we have to show some love (washing) on it from time to time.
Now compared to the chikuhodo fo-5, and this is just my personal opinion (nothing professional here, purely from personal experience) i do not see any difference with regard to softness. They are both super soft, if one is softer its unnoticeable, well from my perspective. But i still prefer Z-5 because it is flexible unlike the fo-5 which has some resistance. Resistance, meaning fo-05 does not flex or cling on my eyelid. Z-5 bends and hugs my eyelid, splaying more than fo-5.
Because i have wrinkled monolid and few milias (small bumps) using Z-5 spreads the eyeshadow evenly because it clings to the entire surface of my eyelid. I find that I reach more for my Z-5 than the fo-5. The added feature of Z-5 is, I also use it to sort of erase or diffuse the shadow if I overdid one eye, without causing irritation. I can swipe my lid with it several times without feeling anything.