I have a 6440 and a 6430. The manual and accessories are easy enough to acquire.
The main problem with that series of machines is that the fixed gear that the cams slide onto is prone to cracking. It's an easy enough fix, but the gear runs about $75 or so. Another issue is that the grease they used really gets stiff with age, and things don't work right. The two I have had stuck reverse sewing mechanisms that had to be unstuck.