I got my Vintage Singer Zigzagger! Big Disappointment!

I got my Singer Zigzagger yesterday, I am very very disappointed about this attachment.  I tested on different fabrics, changed different tensions, played around with the setting.  But the results are the same, the stitches are way too inconstant.  Sometimes it looks perfect, then suddenly it looks very crappy. 

I should read more before I bought it.  After I won the auction, I read my vintage Singer Yahoo group, ppl complaining how crappy and useless of the Zigzagger.  :(   I may try to sell it at Ebay.