It's a trade-off. The ankle pick requires you to get lower and has some of the disadvantages you mention. On the other hand, it can give significantly more leverage for pulling someone's leg out from under them.I don't understand why people like to use "ankle pick" instead of "knee seize"?
- You have to reach much lower to your opponent's ankle than just to reach behind his knee.
- If you drop your knee down on the ground, you lose your mobility.
His left hand only have to move 1/2 of the distance o reach behind his opponent's knee. If he drops his right knee into his opponent's groin with his body weight behind it, it can be a good finish move.
By using knee seize, you can take your opponent down and then take off. You can't do that by using ankle pick with knee dropping.