I wanted to upgrade from 1.5.25 to 2.5.1 and everything broke down and I had to reinstall my site using Akeeba backup.
Then their support migrated my database for e and sent me a migrated one but i still didn´t work. The menues where corrupt and every alias also, so the links didn´t work. I tried three times and then I gave up.
I tried Jupgrade instead and when my webhotell turned off the safe_mode everything worked very nice. Conclusion: Don´t spend money on SP upgrade Use Jupgrade instead.