Have had a fair amount of queries about the lens and have answered them in bits and pieces over PM/Mail/Phone.
Trying to put all of that in a single place for the benefit of the forum
Pros -
1. Great value for money in terms of reach. The cheapest way to reach 500mm.
2. OS pretty decent. A huge difference when it comes to handholding
3. A good bargain for a bit of "Active" shooting...very hand-holdable
Cons -
1. IQ not that great, the closer to full frame and/or subject, the better the IQ
2. Hunts in low light and low contrast situations (but hey! that is true with most of the lenses

)
3. AF accuracy can be a bit of a hit/miss when the distance to the subject is large
4. Heat in the field affects IQ (possibly due to the lens barrel design). Needs a lot of care to keep the lens protected.
As with all lenses, this lens too does take a bit of understanding. A few tips from my experience using it -
1. f6.3 is more close to f7.1 since the lens reports a lesser F number to maintain AF - so your exposure compensation needs to be accordingly set
2. Works great at close ranges which means it does a great job of magnifying the subject. Not that great at long ranges most times - as it tends to lose definition on the subject.
3. Turn OFF IS when shooting in good daylight, found the IQ improves
4. Till 440mm, stopped at f8 gives decent results
5. If you "have" to use it @ 500mm, f9 and beyond only please
6. Works better at higher SS "without" OS turned on. At lower SS, the OS does a decent job
Use IS for shots only below 1/320
7. Work on handholding techniques - if you're not using any support
8. Use OS mode "2" if you need to, does far better
Not exactly the fastest of lenses, but once you've given time to understand it and work with it, gets a little easier to even track down BIFs.
Does hunt a bit in low light, but the FTM ring does help to bring it to lock on a lil faster
Others who have used/are using this lens, please do add-on
Cheers,
Hayath