I obtained my 100-400 L IS from a friend of mine.
Not knowing muck about the Push-Pull design, I was a little concerned at first. After a few minutes and all concerns were gone.
Every time I use the 100-400 L IS I start humming Tommy Dorsey and Glen Miller tunes.
Canon 5D Mark III (x2), BG-E11 Grips, 7D (x2) BG-E7 Grips, Canon Lenses 16-35 f/4 L IS, 17-40 f/4 L, 24-70 f/4 L IS, 70-200 f/2.8 L IS II, 70-200 f/4 L IS, 70-200 f/4 L IS Version II, 100-400 f/4.5-5.6 L IS Version II, TS-E 24 f/3.5 L II, 100 f/2.8 L Macro IS, 10-22 f3.5-4.5, 17-55 f/2.8 L IS, 85 f/1.8, Canon 1.4 Extender III, 5 Canon 600 EX-RT, 2 Canon ST-E3 Transmitters, Canon Pixma PRO-10 Printer