IMO you want a 24ft carbon telescopic pole squeeks, no 12ft pole will ever do all tops, i couldn't reach most of my tops with a 12ft pole. 18ft is usualy good enough for most domestics but (as far as the facelift anyway) you never even notice the extra section on & it's dead handy to have the extra length.
You'll regret buying a cheap flexi glass pole, you'll be using it all day, it's your main tool, don't skimp mate if at all possible.
tony