Well, last time I checked, the NTF have lines voiced in one go. HECU units have words recorded and those words are combined together, making a more artificial-sounding voice but more lines with less effort. Also, NTF do not terminate on-site personnel, HECU do.

tbh the general reason they're there is tho

Yeah.

And also, SCP CB has multiple endings. Half-Life has one.

Yeah