ok I have a 669eco. The 669 is the best machine in its class in the world. Only Seiko makes a copy of it and it is not as good for about the same price. i can tell you who has the best price on it.
You can add a air foot lift to the 669 eco. I have done it and I can walk you thru setting it up. You can use a speed reducer on a 669 eco with a servo motor but cannot add needle positioner because the speed reducer screws with the needle positioner sensors. You can add LED lights to it. I have 2 different lights on the machine.
You can sewing bindings with the machine but that means new feet, throat plate and feed dog plus the binder. You can make it a symmetrical feed binder. contact me.
glenn