The biggest difference between the two keyboards is that one is 104 key and the other is 87 key. The others are basically the same. They are both cherry shaft bodies, replaceable upper covers, and steel plate tuning.If you need a numeric keypad for daily use, the A840 is more suitable for you. If you have no need for a numeric keypad, buy the A87.
I don't know who is cost-effective. The keyboard is a consumable. You can choose it according to your own needs and pocket money. If you can, you can experience the feel. You can choose it as long as you feel good.
