[marfish]

Tumble (Melee Attack): Your advantages combine to give you the chance to not just hurt your opponent but bring them to the ground. If the damage being inflicted on a target is greater than the target’s Body, they are brought down, giving them the Prone status. Cost: 1 Edge

I am confused...what the point of this edge action? standing up is just one minior action that I can take in my turn without doing any test...So...I just spend an edge to potentially exchange one minior action of the opponent?

[Reaver]

Don't have the 6e rulebook, but I would suggest you check out the "Prone" condition modifiers....

If older editions, being prone fucking sucked! Defense actions were limited (later changed to a DP modifier), attacks against you had bonus dice, movement was limited until you stood up (so getting into cover was harder)

In 4 and 5e, knocking someone prone was mostly a team taxtics thing, because of the limit of a single attack/rnd.... which meant a team's first attacker would try to knock a target prone, thus limiting that target's defense and attack dice pools, while adding a situational bonus to the rest of the team....

[MercilessMing]

The way I've run this in the past is applied the 2 meter move limit from Prone even if they spent an action standing up.  That gives more utility to tripping and tumbling.  So, it can be useful to control a target's movement if they're trying to run away or charge a soft target on your team.

edit:
Tumble DOES need clarification though.  Here's the text:

Tumble (Melee Attack): Your advantages combine to give you the chance to not just hurt your opponent but bring them to the ground. If the damage being inflicted on a target is greater than the target’s Body, they are brought down, giving them the Prone status. Cost: 1 Edge

The damage that matters is the potential damage of the attack, in other words after the Defense Test and before the Body soak roll.
Characters are always knocked down if they suffer more damage than their Body attribute in an attack, after the soak roll.

[Xenon]

what the point of this edge action?

To cause the Prone Status Effect (which cause a negative dice pool modifier of 2 dice while defending against attacks from Close or Near ranges and typically also cost a Minor Action to get rid of). It is perhaps not an instant "I Win"-button, but for just 1 Edge it is not too shabby in the right situations ;-)

standing up is just one minior action that I can take in my turn

The Stand Up Minor Action can only be taken during your Turn. Until you do you will still suffer the Prone Status Effect (perhaps your attacker started with Tumble and then followed up with a second attack or perhaps he got friends that can now attack you while you are Prone). And when it is time for you to act you need to sacrifice one of your minor actions to Stand Up (which perhaps mean that you no longer have enough Minor Actions to attack twice).

[Hobbes]

A melee attacker with potentially a second attack or with friends in melee?  Knock prone, buff the next couple whacks on a target?  Pretty much it, but it's only 1 Edge, so it's basically a freebie if you're earning edge on your attacks frequently.