I would expect the resulting java code to be very 'mechanistic' in its implementation. I would be impressed if the code followed any appropriate high-level design patterns, or be as concise as hand-written code <b>could</b> be.
You'll probably have to go in and tweak some of the Java.
One important aspect of good OO design is to 'encapsulate what varies', or is likely to vary. How would a conversion tool be able to tell what bits might vary? That's something only humans with a design plan would know. This could lead to maintenance / future expansion problems.
I would get an evaluation version of the tool and try it out.
To sum up my overall opinion of tools like this:- Machines can produce code, but it takes a human to produce a good design which good code can flow from.