The main point of the Gadgets is to keep hand advantage. When you summon one Gadget, you can use its effect to bring another Gadget to your hand. Therefore, each turn you can keep summoning at least one Gadget per turn, while your opponent, over time, will most likely run out of monsters to summon. When you combine the Gadgets with Royal Oppression, your opponent will only be able to summon once per turn (since you can stop them from Special Summoning), so this gives you both hand and field advantage. I hope this helps!