By now you’ve learned what you need for an effective testimonial:
1.  OBSTACLE . . . that prevented action with you in the first place
2.  RESULT . . . enjoyed as a result of actually using your service/s
3.  KEY ELEMENT . . . that produced the result enjoyed
4.  KEY BENEFIT  . . . your service produced for your client
5.  ADDITIONAL BENEFITS . . . easier once the first one is defined

So your last question, “Is there anything else you’d like to say?” may (or, may not) provide something new.  But, you never know until you ask!

I interview people for articles I write and I like to use a similar question after I’m ready to stop.  Funny, but simply asking, “Anything I did NOT ask that you’d like to address?” often generates some of the best parts of my interviews.  Not always, of course.  But often enough that I’ve trained myself to pose that question to someone I’m interviewing.

KEY POINT:
When you think you’re ‘all set’, remember to pose this final (and sometimes very revealing!) question