I was choosing between M16 PRO and Z13 XTM as they have the same price point and features, I bought the Z13 XTM for its all mesh feature and lumbar support as I work from home and have a scoliosis which gives me pain - as I'm getting older and less fit I can't afford to ignore it, and skimp out on getting an ergonomic chair, so I finally bit the bullet and plumped for this one.
Looks: Really professional, the mesh has a little pattern on it which makes it look a little bit more interesting than just plain black, the stainless steel wheel base matches my bar stools in the kitchen which is a nice touch. I thought it might look tacky and cheap but it actually looks really good.
Comfort: Mesh seat and back are soft and bouncy, and let my skin breathe, when you've got a deploy deadline and you know you're going to be stuck to your chair for 10-12 hours it's necessary. The arm rests are also slightly padded and you can move them further in or out, back or forward, or turn them on an angle. I use it for gaming sometimes too so it's great I can adjust the arm rests.
Back Support: The adjustable lumbar support pad is amazing. The head rest is sturdy, and comfortable - I didn't realise how much I strained my neck without one of these and it's adjustable.
Armrest: highly adjustable 3D armrest as opposed to M16 pro with more restrictive 2D armrest.
Height: Goes up nice and high, as a 5'7 woman (not even that short) most chairs are unfortunately built for men, this is the first chair I've been able to get low enough to place my feet on the floor comfortably.
Build: Really great quality, very heavy and sturdy which is unusual as everything is normally cheap light crappy plastic which breaks.
Bonus points: Super quick delivery, assembly took about 5 minutes as it's half assembled - you might need to get someone else involved to hold the seat and mechanism as it's quite heavy.