String Swing BCC04TWN-V-UK Twin Hanger for Mic/Music Stand - Violin & Ukulele/Mandolin

Will this item hold all sizes for ukulele?

I ordered one and one size fits my one uke, but the other uke is too wide. Is there another holder I could screw in, or another size, or an adaptation

will a 2nd grader's violin fit the twin Violin/Ukulele hanger or should I buy the "small violin" hanger and one for concert ukulele?

What is the platform jutting out from the front (or back?) for? (Rosin? For a ukulele?)