Listen, all sage advice aside, you are most likely going to like the TE. The second generation w124 cars are a very nice drive. They are a much more modern chassis than the w123 or w126.
However, just ask yourself: If it's such a great car... why does he want to trade me for an older turbodiesel chassis

?
You may want to beam on over to the gasser subforum and ask some questions about TEs....