Ex-25 or Raynox 250?
Last i remember the AF won't work with all lens for EX25 and some doesn't even allow you to achieve focus. there's a table here http://www.four-thirds.org/en/pop/extension_detail.html that gives you all the details of this extension tube.
If you want convenience, I would think the raynox would serve you better.
It give 10X magnification mountable on all lens lens with filter diameter 67mm or less and quality of the lens is very good indeed without the light loss of EX25 as it's an achromatic lens. Best use with a telephoto lens if you want more magnification. Note it's not an easy lens to use and hand holding at that magnification is very very challenging.