That is a great combo, but let me compare it to another I recommend you try out.
1. stun > MFD DFA > vanish garrote/CS > envenom
2. Vendetta/MfD macro > envenom > vanish > envenom
The advantages of #2 are as follows:
*you do not waste the enemys stun DR or put your kidney on DR.
*you x2 envenom directly out of stealth, so very burst oriented.
*you do not waste 85 energy or the 3 combo points given in combo #1 when you are already point capped from vanish.
*Vendetta/MfD macro is clicked pregame so this burst is 3 globals instead of 7.
#2 would require Nightstalker to make each envenom hit as hard as a DFA but with this both envenoms will be a 100% crit instead of just one. It's also fast movements so you can squeeze as much damage in as possible during the shortest timeframe.
I hope this assists in you owning people
PS: Prey on the Weak is good if you have a great partner and coordinate properly. A higher skill cap is needed In order for it to be as effective as Internal Bleeding. Internal Bleeding gives you one of your strongest dots plus it's free damage that can be applied in any dynamic situation, so its environment friendly.
Prey on the Weak also requires you to use abilities like Vanish to get a CS or the use of your kidney to activate. This leads to a style of pulling energy so you can burst into a stunned foe. I feel Internal Bleeding helps you manipulate the battle field better as it compliments the natural flow of battle.
Some examples of this would be:
*Using kidney to pin and beat on the kill target while recovering the energy you just used with Burst of Speed to get to him/her in kited scenarios.
*after a vanish being able to go directly into the 5 point envenom instead of CS > envenom. Not only the wasted 40 energy but the time and globals needed is huge.
*In a fight were you use kidney for a peel or CC you don't waste the Prey on the Weak effect. Instead you turn it into a possible kill. You always get enough dagger hits off to apply Deadly or Wound poison when you kidney. When you kidney use the +25 energy from Relentless Strikes to apply a Rupture. Rupture is crap damage but Venomous Wound is solid. This means that when you jump back on the main target and all eyes are on that target whoever you used kidney on is going to be rotting with Venomous Wounds, Internal Bleeding, Rupture, and Deadly Poison if you run it. This leads to a PERFECT hard swap out of knowwhere in a smokebomb as they can get to -75% without even realizing it. People watch their health bar when lock dots are on them, against a Rogue unless the Rogue is on them they never think to check health because statistically they don't need too.
When you watch streams and see "HOW THE F@CK DID I DIE?!" shenanigans like this is normally the culprit.