I have had various of these over the years, extreme extension was one, another one I don't recall the name of - they have mostly worked fine, subject to noting one point below. When I needed to replace one recently (because my new router motor has a different thread), I looked again at them all and chose the Musclechuck, available in the UK via Woodrat
http://www.woodrat.com/chuck.html. If you look at the blurb (see the US Musclechuck site), I think I was persuaded that the design of this Musclechuck was somewhat superior to the other similar products, the full details I would need to remind myself on.
The point to note is particularly important when using the 1/4" reducer and that is to line it up in the collet so that it is squeezed rather than just crushed by the cam/screw, otherwise it will slip and can come loose.
Definitely makes working with a router table (or the Woodrat) much easier.
Cheers