I have searched this topic but never got a full proper answer. I bought a DG-250 about a year ago and the guitar had to be sent back to Saga due to some issues. Then i got it back with the completely wrong bridge, i was so mad so I sent it back again. I got it back and the neck was completely warped and there were other problems. so i sent it back again and, when i got it back...there was a huge crack in the headstock.
Furious, I demanded they send me an upgraded version of the DG-250 and they agreed, sending me a DG-255 by next-day air. However....isn't the DG-250 and DG-255 THE SAME MODEL? In fact the DG-255 is always listed a little cheaper and some sites have different specs on it than others! I checked the djangobooks.com specs for official details and I still can't figure out WHAT is the difference between these two guitars besides the fact that the 250 has a 'solid peghead' and the 255 has a 'slotted peghead' (what does that even mean?) Now I'm really mad that not only did they practically send me the same guitar, but possibly a WORSE one with more problems!!
The DG-255 slotted head refers to the construction of the head stock which is similar to classical guitars, and the solid head stock resembles most of the acoustic guitars of the modern era. (See pics below) I don't know that any one is more favorable over the other, though. Both style head stocks were used in the SelMacs at various points. I prefer the slotted head stock just because - I like it.
I found this table summerizing the Gitane line of gypsy jazz guitars, well most of them anyway. Hope it helps, and hope you get out of the dumps and get a proper replacement soon.