I've been using the variant 20, 20, hit from the DMG for the last year that I have been running my campaign with 3 different groups.
It has never come up in the countless hours we have played. Yes a double 20 has been rolled, however the follow through has never resulted in a hit. Players start cheering when that second 20 comes up and all wait expectantly for the third roll. But never has it happened.
I do have a house rule in effect though regarding -10 hps. You stay at your negative hit point total for a full round of actions. If you reach -10 you cannot stabilise on -10, so you have to be saved by someone else. This adds to the tension of a combat.
Of course with the super kill option, I have a super fumble option.
Roll 1, 1, miss and you're going to regret it miserably.