Can anyone tell me what the deal is with these two EHX stomp boxes?

Ive heard that the Double Muff is basicly 2 big muffs put together, so why is it less expensive?

I dont know whether to buy a big muff on its own, or buy the double muff for cheaper. Surely there must be some catch when buying the cheaper double muff. Is something lost in the sound quality, or certain sounds not as easy to find on it. its really confusing me, any help would be appreciated, just explain what the deal with these two pedals are.