The Kahr site explains "U" marked guns. I'd buy one if the price was right. Typically they are in excellent shape and any problems should have already been discovered and fixed. T9s are hard to find, so if you have an interest in one, and the price is good, my advise is to consider it seriously. I'd look to pay around $600. It may come with only one mag as opposed to the two mags a new T9 would have.
I do own a "B" marked Kahr. B is for
Blemished, a gun with a cosmetic flaw. I can't find it if it has one and the gun , a K9, has been 100% reliable. It's one of my favorites.
Kahr site explaination here.
http://www.kahr.com/faq.asp#q26