I. If they own the trademark, you are in the wrong. All you did was change the country code extension on the domain. Furthermore, you are using the same name for the same type of business. Look up legal cases and you’ll see how you will lose.
II. If they don’t own a registered trademark, they still own a common law trademark. It’s less powerful, but it still exists.
III. Don’t try to get smart. If they take you to court, and win, you will end up losing the domain. You will get nothing. On top of it, you will be out money for your own legal defense and you will also have damages assessed against you, which will include their legal defense. $600 is going to seem like a mountain of cash when it’s all over.
IV. If you don’t like their offer, ask them for something else. While you are at it, hire an IP lawyer. Following some of the advice you find in forums is going to get you in plenty of hot water.
That case is not even close to being the same issue here.
That’s one way to give them even more favor with the court. Not a good idea.