RPG Books a 5E DM should get

So as a new 5E DM, who's only started playing D&D, I have the three 5E books.



But while at Barnes and Noble, I noticed they had the AD&D books (Second edition?). They had the Monster Manual, and it looked pretty neat. It made me wonder if maybe I should buy it and if it would be any help to running any version of D&D.



At the very least, it could give me some ideas. Are these worth getting?



Also I noticed there were many Monster Manuals when looking online associated with AD&D. Monster Manual, Monster Manual 2, something called a "Monstrous" Manual. What's the difference between a Monster Manual and Monstrous Manual?



And how different are the stats of creatures between games? Would you be able to port a monster over from one edition to the other fairly easily?

RPG Books a 5E DM should get