I have one. I mostly use it as a straightedge when I need to scribe a line that's longer than my ruler.
Occasionaly, I use it for what it was intended, as a large clamp. I works, although you cannot tighten it really hard. My guiderail combined with a FS-Rapid/1 set acts as my second large clamp.
I'd recommend to get yourself another guiderail with a FS-Rapid/1 set instead of this. If you really want one you can have mine in exchange for a good 1400mm guiderail. [big grin]