If this is the Kurvenlinfix or similar to I ordered one of these about two years ago and they are awesome! I have used it several times to make arched top face frames for open book cases on built ins. Trace the curve you want, cut close with a jig saw, secure it down with the screw provided and then a quick pass with a pattern bit and walla perfect arch every time. Would highly recommend this if you do curves or arches on a regular basis.
TIM