Change your preferences here.
Reduces Speed 50%. Doubles EVs earned.
Macho Brace halves the Speed of the holder, something that may immediately appear disadvantageous; it does have its uses, however. It is very comparable to Iron Ball, which has the same effect, but also removes the Flying/Levitating effects from the holder.
Macho Brace makes for a good item to Trick, as it cripples essentially anything without risking passing on something useful, such as Choice Scarf. It also powers up Gyro Ball and is useful on some Pokémon in Trick Room, which otherwise risk being outsped. It also has an advantage over Iron Ball on Pokemon like Bronzong, as it does not remove their immunity to Ground-type moves, Arena Trap, and Spikes.
The most immediately obvious disadvantage is that it makes the holder incredibly slow, leaving them vulnerable; however, it only sees use on slow Pokemon such as Bronzong to begin with. Unfortunately, these Pokemon desperately miss Leftovers recovery, although they can potentially obtain some with Trick. Although Iron Ball is disadvantageous for the holder, its side effects are particularly problematic for the recipient when Tricked; Macho Brace only halves Speed, something that might not end up useful against slow sweepers / walls, anyway.
Pokemon with Gyro Ball, Trick users, or Trick Roomers are the only effective users of Macho Brace. Keep in mind though that the Base Power of Gyro Ball caps at 150 (excluding STAB), and these Pokemon are generally very slow anyway.