This is the best review of the PL-660 that I've come across:  http://radiojayallen.com/ tecsun-pl-660/   Jay's reviews are typically very thorough.

In my opinion the Synch-AM mode on the PL-660 is fairly useful, particularly on fading shortwave stations. However, the Tecsun's Synch-AM is well below the same mode's performance on some other receivers (ICF-2010, E1XM, AR7030 come to mind).

Unfortunately, this radio is a disappointment for BCB DXing... unless, of course, you perform a Gary DeBock-style monster loopstick transplant on it! 

73,

Guy Atkins

Puyallup, WA