I've had my extreme 18 for a month or so now, and it hasn't worn even the tiniest bit.
It's the best pole that money can buy in my opinion. I've previously used an slx 25 and clx 18, now it's a real pain having to use them instead of the extreme.
I will be buying an extreme 25 very soon.
If you are heavy handed and don't want to spend the 15 mins at the end of every week washing the pole out and cleaning, then stick with slx.
But if you want to use the best pole out there, and are happy to maintain your equipment, then you will love the extreme.
Also if you have any aches or pains at the end of your working day, you really should switch to extremes.