I was under the impression that the 120 and 120B design on the tuning end of business was the same and that the scope was the difference.
No, not just the scope. It was the other design changes, "updates", that were unsuccessful in the 120B, from a performance standpoint, and, therefore lead to the quick update to the Model 150/125. Check the relatively short production period of the Model 120B.
Either scope was not an issue in terms of performance. Actually, from a purely cosmetics aspect, I prefer the look of the Model 120 over all the rest. I don't particularly like the larger tuning dial 'window', as in the transition from the 2270 to the 2275 receivers, and 120 to 150 Tuners. Many disagree; but I find the newer Models are too 'busy' looking. The new models lost some of that earlier Marantz elegance in favor of MORE knobs and switches. With the Model 2275, the 'receiver Wars' were on. The new bread of receivers had to be MORE Powerful, with MORE features, and 'LOWER' THD and IM Destortion, at least the marketing dept seemed to think so...
As an example... as good as the Model 150 is (with the larger scope CRT and tuning window), the Models 20 and 20B (both with the smaller, out of production CRT) remain superior tuners, in spite of their age.
Of course, when recommending a first tuner, the age of the 20/20B will frequently present restoration issues.
I'd feel safest recommending the 125 and 112 to a first-time buyer, especially if cost figures into the decision.

I currently have a Model 150 and 20B in regular operation
in the livingroon and my home office/den. Guess which one gets played the most.

I keep a couple Model 125 and 120 as back-ups.