[Electronic M]

That set is a regular monochrome NTSC TV. As long as you don't remove that adapter plug is it no different from any other average monochrome TV of it's time.

Those adapter plugs weren't even wired into the TVs circuits on many makes and models (it was just a gimmick to convince the customer that was reading about color development in the news that his expensive new TV wouldn't be unusable in a year or two).
A few makes did connect the color adapter plug into circuit. Sometimes the block-off plug had some jumpers to open sweep time constant circuits to allow the adapter to change the sweep rates, other times the plug is effectively just a collection of test points for various signals and power supplies.

Most makes that sold TVs with an adapter plug never sold an actual adapter.

TLDR: that adapter plug is a probably an historically interesting marketing lie, and that is a normal black and white tube TV.
If you work on and collect normal black and white TVs this one should be the same but with some interesting color TV history talking points associated with it.