I wanted lens with better resolving power at distance than the sigma 70-300 APO macro 2 which I already had for my Canon 300D. I missed a good 2nd hand Canon 300 F4 prime, couldn't afford a new (or second hand) canon 100-400 LIS and saw a review of this lens.
Checking out it seemed to be the best lens that nobody was talking about so I took the plunge and purchased it.
At first I was worried about the weight (I'm in my '60s and a bit arthticky) but after a while I learnt to handle it. I usually carry it with a monopod attached via a ball-head which lets me tuck the shaft of the monopod under my right arm. This acts as a brace and I find I can now carry the lens for 3-4 hours without problem including some shooting from hand as well as monopod.
So far it has done everything I want of it, including getting me some reasonable shots with stacked EX 1.4 and EX 2 xTCs.
Playing recently I find I can also get good close-up shots using 65mm of extension tubes. A tripod is essential for this however.
So, in my view, a great success at a very reasonable price, strongly recommended if you can't afford Canon L glass prices but want good results