Here is a legality question for you :

[Simon]

Here's some info that may help a little, though it would be better to get a real legal opinion before you actually use comparative advertising, even in testimonials from customers.

Fair comparative advertising has long been permitted under U.S. law. A summary of the law regarding comparative advertising can be found online at http://www.ftc.gov/bcp/policystmt/ad-compare.htm. Comparative advertisements must comply with the same rules for accuracy, fairness, and substantiation as other types of advertisements. Failure to properly substantiate comparative advertisements can lead to defamation or disparagement claims. However, assuming the comparison in the advertisement is accurate and fair, it is appropriate to identify the product or service to which you are comparing your product or service by using its trademark or service mark. However, you should use only the name of the compared product or service and refrain from using any stylized logo, design, or slogan. You should also avoid using the competitor’s mark more than is necessary to make the comparison.

These searches will get you some of FTC regulations/guidelines you have to consider too...

http://www.google.com/search?q=using...dvertising+FTC

http://www.google.com/search?q=using...estimonial+FTC