First of all: What is this "ü" in the logo?

The “ü” is a German letter, called umlaut-letter. It sounds like the french spoken “u”.

If you can’t pronouce it: Doesn’t matter. Take it as an u then. We will understand you. The rest of the name (Lunstroth) is still complecated enough. (The “h” at the end isn’t to be heard. So, something like “lunstrot” will do.)