Yeah I don't really like how special executions work. As soon as the button is pressed there is no saving the person, even if the executioner is shot before he finishes getting him down on the ground. I've seen so many times where someone is being revived and a guy runs in and executes the him mid-heal, then dies immediately from point blank shots to the face by the would-be reviver.
Ultimately it just encourages bad gameplay because the executioner don't suffer any penalty when they get killed during executions except having to wait for respawn, so everyone just runs around executing anyone that they see is down, when usually its better to just wait for them to bleed out on their own so that their teammates are distracted and possibly lured out for an easy kill.
It's kinda funny seeing someone get their head bashed in or blown off by nothing lol...
But it's risk vs. reward. Yea you can run in executing the guy, but get killed in the process ultimately trading 1 life for another. It's a lot smarter to use them as bait for people to revive them, or execute them from afar.
The special execution is implemented perfectly. It uses an animation to look cool and make the reward not only functional (extra parts)but also visually appealing. If the special execution was made so that you could stop it half way through people would complain that they would rather just shoot their head off instantly for a special execution. What bothers me about it is when you down someone and you stay in a defensive position while you let the downed player bleed out, your teammate goes running into the open to special execute said downed player and not only takes your execution but gets killed in the process so your excution becomes meaningless to the team.
They should have a separate stat for people that execute someone but didn't take away any damage to initially down the player. Something like a team execution or assist, in which it still counts as killing an enemy but it doesn't give a parts bonus. So that it helps the team be closer to victory, but guys wont be desperately trying to get special executions to boost their stats/parts.