I used to find the Xtreme brushes didn't lsat long when I last used them a few years ago but decided to try the one of the new ones with natural bristles and have found it quite a nice brush.  It works very well on snail trails and is super light.   I've been using it for about three weeks and today I put an Ultimate back on to do a small conny roof and left it on for a short while and it felt like a brick by comparison to the Xtreme.  As to longevity, we'll have to see, but so far I'm liking it for regular cleans and there is very little sign of wear.