No idea of cost Joe, A telepole is a 3 section (like the harris) so sections 4 and 5 are available seperately to order (try "windowcleancentre")
Harris is a 5m so adding a No1 is 2m and a No5 is 2m = 9m.
But its getting heavy again. I got the Unger to 42ft by adding extension to extension, but it reached its limit.
The Zensor will add 3.5m to the 5m harris, Lewis if used vertically and is a lighter way of doing it.
To be honest, Its a good little pole at 5m but by adding bits... well I think I wouod prefer to go the C/f route to get to 30ft because your mixing tele with modular. But it will doand I am having fun with te Harris even though its a 3 year step backwards for me. Only trying to say what will go with what to save folks time
By all means get a harris because its now going to become the first step on the "ladder" but going higher than 20ft needs a different approach and more £££
ps Peters clampless alu may also be worth waiting for later in June as its shorter than the harris which 6ft2" without a brush when closed -