No pros and cons they are two different techiques. The first is a traditional "thump" and the video does not actually correctly show how that is done. Your thumb sort of "goes thru" the string and ends up resting on the next string. Classic thump. The vid shows him kind of bouncing off he top of the string. I wont say its "wrong", but its not what a master of slap would teach. ( I know for a fact).
The second technique is double thumbing, and it's more like using your thumb like a plectrum. Up and down. It is NOT a thump. Its designed for speed, like picking 16ths.
If you're serious about slap, check out Anthony Wellington's courses at
www.musicdojo.com Yes, it costs MONEY, around $50. But its WELL worth it. He teaches three progressive levels. Yes, its online, but you send him your work and he will critique it.
If you care to learn from the best, he is available. Maybe the free 5 day class can access Ant.
