Well, I'm no fan of extensions. I used to play a lot of snooker, and I had a very good snooker cue with extensions that were high quality. I never used them unless they were needed even though I played on a 6*12. I also had a very good custom made extension for my Mezz. Used it on stretch shots and only on those. All extensions change the way the cue feels. I've never tried one that didnt'. You may of course LIKE that the hit changes, I just happen NOT to like it. The smallest Mezz extension does change the feel only minimally, but still noticably to me.
For a period of time all the pool junkies at my pool hall had extensions full time on their cues. Now almost all have taken them off. The ones that kept them are either very tall, or only have a very short extension. The best players all took them off. IMO it's a fad that will go away.