I had the pleasure of trying out the 600mm mkiii which was kindly sent down from Canon, the first thing i noticed was the weight, well lack of it, with one hand and a 1dx strapped on you could easily lift above your head and move around. With the insides all moved towards the collar it was balanced great and made it a lot easier for hand held. My mate Andy tried all the hand held test as I had broke my shoulder at the time but still managed to use for 4 days with one hand. Focusing was quick, presice and silent, quieter than my mkii The 5 stop stabiliser worked great at hand held and on a monopod. All my shots came out sharp. The focus ring took some getting used to as you have to engage the focus first and then use it. Is it worth the money?, well for a 600mm hand held and portable , I say "yes". It was amazing. Many thanks to T4 for arranging all this, you won't get this service if you buy online!!