I don't like it, specially if this is something you do frequently. The main reason is that not all identical RPM slip generates the same amount of heat.
From factory during normal driving cruising along the computer will send between 20-40 psi to apply the clutch and keep it at the 20 RPM desired slip rate. But now will all that torque applied in order to keep it from slipping you are ramping up the pressure to roughly 100 psi and this applies to a piston with a huge surface area, so that's a lot more force there. To give you an idea how much difference it makes, the piston surface is roughly 93 square inches, so we are talking 1,260 to 3,720 pounds of force on that piston and now going up to 9,300 pounds! As you can imaging that same 20 RPM of slip will generate much more heat under so much more force. None of the components in there (piston, lining, cover) were ever designed for anything like that, I don't know how long it will take before one or all three gets damaged. All in all, if you are going to do WOT pulls and keep the lock-up apply, you really need a different converter.
Talking about the force applied to the converter clutch piston, here's something that might help illustrate why it is a problem. GM has been using ECCC converter clutch strategy since 1996, so nothing new here with the carbon woven lining and the ability to have 20-40 RPM of slip constantly without it causing any issue, but on the 6L series they added a new twist. To help provide the computer with finer precise control of the slip rate they started using a tapered piston instead of a flat one. The way it works is that at first, only the outside edge of the lining is applying. As the computer increases the apply pressure to reduce the slip, the piston flattens out and now the whole surface comes in contact with the cover. In the pictures below, the image on the left is before force is applied to the piston, and the picture on the right is once pressure is applied flattening out the piston against the cover.
Tapered.png
Notice how little the gap is between the piston and the converter cover in the image on the right with some force applied to the piston flattening it out? Now imagine what happens when someone goes in an change the tune to try and make the clutch have zero slip even under heavy load. The piston does not stop flexing, with enough pressure (which it was never design to have in the first place), the piston ends up bowing enough to touch the cover. Once that happens it does not take very long for the whole thing to self destruct. With a good quality aftermarket converter you will have a new billet cover AND a new flat billet lock-up piston that can handle the extra pressure and a lining that provides a good seal and easily lock instead of the factory woven type material that can never seal completely, so going to zero slip, even under heavy load is no longer a problem.