I've owned too many Mopar vehicles over the years to count. Each and every one of them that had a Torqueflite 904 or 727 based transmission had a shift kit or shift improver kit added as soon as it came home from the dealer. This included later model over drive equipped 500s, 518s, 42, 44 and 46 RH and RE models. I have installed shift kits in some 47 and 48 REs as well. In all cases the object of the game with the kit was to increase line pressure, there by increasing the clamping forces of the internals and to delay the up shifts. It seems to me that if the Sonnax does this, that is what we want.
As far as the increased pressures casing more wear, this should be offset by less wear on the internals because the slippage is reduced. Ad to this that if the truck is being driven in a spirited fashion or towing a great deal, one must step up the maintenance. Oil and filters are less expensive than components. JMHO.