I looked into the defference between the two types of leveling kits (spacer above strut assembly vs. pre-load spacer) quite a bit before I had mine done. The bottom line is the type that puts the spacer above the strut assembly can over-extend your lower control arm and increase the CV joint/ball joint angle when the suspension is fully extended. The pre-load spacer will not do that. Although when your truck is just sitting there or during normal driving conditions your truck will not know the difference between the two types of lift. The CV/ball joint angles will be the same for each type of lift as long as they are the same hight lift.
My Revtek leveling kit is a 2.5" in front and 1.25" in rear. After the alignment and it settled in it gave me 2.25" higher in the front than stock.
You should read the comments "Russ" made at the bottom of this Truxxx Kit review -
Truxxx Tundra 3" Lift Kit Review | tundraheadquarters.com - Russ sounds like a really smart guy!
With all that said a level kit is going to be more harmful than a true lift kit. A true lift kit will equalize all of the increased angles of your suspension except your driveline angles.