I am very interested in an MD's perspective/opinion in regards to the difference in the Palomar 500: 1440 & 1540 hand-pieces?

Iv'e read the Palomar Medical site, but I want to hear a professional opinion from a Dr. that has physically used both hand-pieces, & what the difference is between the two. Is the 1540 hand-piece better, stronger, or more effective than the 1440 hand-piece, & if not, what is the difference between the two? OR was the Palomar 1540 hand-piece produced just so Palomar-Medical could compete with the *Fraxel: 1550 Restore* by Solta-Medical?