When zooming in, you are literally pulling your camera away from you and when zooming out you are pushing your camera into your face. Plus, I had to change the way I hold my camera. I usually zoom using a finger on my left hand while cradling the lens in my palm...this wasn't possible with the 100-400. I shoot in manual mode and I'm constantly changing aperture and shutter speed along with continually moving my focus point around the viewfinder. This technique is second nature to me, but the push/pull zoom was very distracting and I know I missed shots that I wouldn't have missed. I just wasn't as fast with that lens.
In the end, I wasn't willing to change the way I shoot to accommodate one lens. I hope version II of the 100-400 will have the traditional zoom. I would buy it in a heartbeat.
You are aware that there is a tension/friction ring on the barrel that lets you adjust the amount of friction needed to move the zoom position, right? If I need to zoom fast I back it off a little so the zoom action is fast and easy
For MF I like the fact that your hand stays in the same position on the barrel (next to the focus ring!). Also, as the lens gets longer your left hand automatically stays on the long end of the barrel which helps to stabilise the lens.
Just another opinion. I love the 100-400 push/pull
5D3, 5D2, Sony α6000, G16 | SY14 f/2.8, Ʃ20 f/1.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 2.0x III, 70-300L | E-mount: SY12 f/2, 30 f/2.8 EX DN, 16-70 ZA OSS, 55-210 OSS, Metabones SB | FT-QL, AE-1P | FD(n) & FL lenses