I like the ones they market as craftsman series, especially the fact that you can get them with brightly coloured handles which makes them harder to misplace.
I also like the laminated blade versions because of the edge they will take.
I am not so fond of the straight wooden handles because there is a slightly higher risk of running your hand up onto the edge of the blade.
The knifes all take and hold an edge very well. They are all strong enough for any real working abuse.

They are very good utility knives. The red paint was on the old ones to help you not lose them too. The traditional handles were either plain or red painted birch and kind of barrel shaped with an oval cross section.

I don't think the question why they are so inexpensive fair. I think a more fair question is why are all these other knives so astoundingly expensive!
After all, aren't they are still just pieces of steel with handles?

I have a few of the Frost/Mora knives around. I have them in both stainless and carbon laminated versions.

The laminated ones have three layers in the blade. The outside layers are fairly soft and allow the blade to flex and bend a bit. The center layer is very hard and holds a truly wicked edge, but is too brittle to survive without the soft layers.

I don't know if when Mors wrote Northern Bushcraft there were Mora knives with plastic handles. I do know the last time I saw him in about 2003 he was carrying one of the ones with a plastic handle. I am not sure if it was carbon or stainless, likely carbon though.
The reason Kochanski chose Mora was because besides being a good pattern they are very common knife here, just about everyone who uses a working knife much has at least one of them.
The updated handles just make them better.