What I know:
The feet snap on.
Viking started a series of machines, Optima.
They decided to stop making the ones that started with 1xx
and make the models that start with 6xx, starting with the 610
While they phased out the 1xx, the magazine Consumer Reports came out with a glowing report of the 150, and many sewers started asking for it, it was in CR and they said it was good, it must be good!
What was Vikng to do?
What they did: They took the outside of the 610 and just put a 150E where the 610 was, so essintially, a 150E is a 610. Though I do think there are 610s also.
I bought a 150E on ebay and I can see why the 150 got the glowing report. I saw the pic in the ad on ebay and it looked like my 630, and the walking foot and all presser feet fit it too. I think I'm just going to hang on to it if my daughter's newer Singer wears out (which I expect it to)
The 150E does have 'blanks' where the 630 has 3 buttons to push, and the 150E has only 1
The 630 has many more stitches too
I just wanted to know what the difference between old syle and new style was. I guess just to fill in the blanks of the story.