Ubuntu adds features in ways that we find dangerous for privacy. For an example, see [EFF: Privacy in Ubuntu 12.10, Amazon Ads and Data Leaks](https://www.eff.org/deeplinks/2012/10/privacy-ubuntu-1210-amazon-ads-and-data-leaks).
It is impossible to verify the integrity of a Tails USB stick or DVD while running Tails from it. It would be like asking someone whether they are lying: a true liar would always pretend to tell the truth.
Unless proven otherwise, no add-on, apart from the ones already included in Tails, has been seriously audited and should be considered safe to use in this context.