Hi
I have been working with this lens for some eight months now and I got used to it. I too use it hand held 90% of the time. Sure it is heavy but my wife's every day handbag with everything in it a woman needs is about the same weight as this lens and she is not complaining.
So I decided to man up and don't complain anymore.
I also have the 60-250 (modified for FF use, by the way) and I used to think this was a real rocket launcher. Now, however in comparison I think, well, this is really a very handy little walk around number.
However there are two issues about the 150-450 I intensely dislike.
Firstly, the pouch which is supplied with the lens. It is big enough to do your weekly grocery shopping in.
Secondly, the huge 10 gallon bucket lens hood. I think when they design lenses, and in particular this one, they simulate the worst light scenario on a computer by using specially created software. I doubt very much that I will ever use this lens under those conditions, in fact I know I don't. How can I be so sure ?
I have retired this bucket lens hood and instead permanently screwed on a smaller aluminium hood. After a few thousand photos I found it gives me all the physical and flair protection I will ever need. Here is my confirmation, I yet have to see a picture of mine with flair problems and I have shot pics in quite dicky situations. And as an added benefit it allows me to transport the lens, with the hood attached in a neat pouch I was able to buy in Japan. (See attached picture) It makes live so much easier.
I thought this bit of information might be useful to others.
Cheers