Deadlift off boxes (rack pulls) vs. deadlift with chains?

[raw_lifter]

Hi, I was just testing my max and I find out that my lockout is very weak!
I am following russian routines, where is deadlift training mostly one time per week and I dont want to change this thing, because it is working great for me.
MO - SQ, BP
WE - DL
FR - SQ, BP

1) I was wondering, if its ok to add some extra deadlift (with chains or from boxes) to my deadlift routine on wednesday after regular deadlift routine.
Should I do it every training or once in two weeks etc..?
2) I have great dilema, I cant choose between chains or boxes.
Chains are good, because I do the whole movement and it gets heavier with the lockout, but you can never add the extra weight exactly in your weakest spot.
Deadlift off boxes (or rack pulls) are good, because you can set up exactly the barbell to your weakest point, but you dont do the whole movement, sou the starting position of the lift is not natural.

So, any advices?

If you want to see my video, where I am testing my max, there is code of the video - DWu4uFiVrb0 (just type this in youtube, I cant post URLs, because I am new here)

 

[moya]

i like doing mine off the rack to focus on the lockout... also gives my lower back some much needed rest... but i think power shrugs are also great for improving lockout as well... if not better...

 

[lweaver]

I would personally make sure my good mornings are up to par and do some heavy DB rows for lockout strength.