I bought a Task Force 4 with extension when they first brought out the extension, in 2006 IIRC. It was to be my 'tent-for-all-seasons' for the forseeable future. I was well pleased with it. Unfortunately, Mrs B. didn't share my enthusiasm.
These things happen. :?
The canopy was substantially heavier than an equivalent sized F10; made with heavier canvas in either forest green or a stone colour The workmanship was very good and up to BCT's usual high standards. I had them make me a flysheet previously, which is haw I came to be aware of the Task Force series.
I would say the inner not as good quality as the F10 item but there was not a lot in it.
The standard poling is steel and the whole setup is a good bit heavier than a F10 of similar size.
A couple of years ago I modified my Task Force 4 canopy to make a hot tent for a member here. I'll post the link when I've dug it out.
http://www.bushcraftuk.com/forum/showthread.php?t=127121&highlight=hot+tent