As with most article titles that end in the question mark, the answer is NOOOOOOOOO. While the Mac OS X El Capitan beta is humming along very nicely on my Mac, my iPhone is not faring as well with the newest beta. Beta 1 suffered from massive power consumption issues. My phone would last about 6 hours on a charge with zero use and would heat up in my pocket for apparently no reason. Beta 2 has fixed these issues, and i feel pretty good about getting though the day. I have also not experienced any heat at all from the phone, even when playing games for an extended period.
The phone is still very slow though. It can be slow to load apps, seach is inconsistent, and animations are laggy across the board. My high end iPhone 6 Plus feels like a budget Android phone. And no, that's not a compliment.
I'm also having Apple Watch issues. I am simply losing connection between the phone and Watch on a regular basis and have had to restore the Watch to fix the issue. I lost months of activiy data, so I'm going to do a restore to get that back, but time will tell if the connectivity issues remain.
The beta is much better on the iPad. Battery life is great (I've been writing for an hour and a half and I've dropped 11%), the whole OS is very snappy, and I have not experienced any crashes. The only issue I have is cosmetic, as some elements in the new Spotlight and some apps don't behave as they should. Everything works, but alignment and transparencies are just wrong.
And this should go without saying, but you're not getting that much by upgrading your phone. None of your apps are going to work any differently now that you have the new iOS. Developers are hard at work updating their apps this summer, but you won't see them on your phone until the fall.
I'm keeping my iPad on iOS 9 for the new keyboard and split screen features (they're both awesome!), but my iPhone is going back to iOS 8.3 tonight. It's not as bad as with beta 1, but it's still not as good as an iPhone should be.