I'm kind of experimenting with it right now. I've been trying different things in small, less visible, spots on my boots, like around the heel or near the top of the ankle. I've mainly tried stuff on my Kathadin Iron Works cap-toe boots. I like the texture of the leather on these boots and wanted to preserve that. What I've found so far is that both Obenaufs LP and Nikwax darken the leather. The Obenuafs though leaves and tacky / sticky texture. This seems to lessen after a few wearings but doesn't go away altogether. The Nikwax leaves a nice smooth finish. Both change the look of the leather but right now I like the Nikwax better. I've also noticed that even though water doesn't go thru, when the Obenuafs gets wet the leather looks wet and water doesn't bead up. With the Nikwax water just beads up and rolls off. Nikwax is much easier to apply as well. (I'm using the waterproofing wax that comes in a tube.) After a few minutes I did need to go back with a clean cloth and get the built-up wax out of any seams or crevasses.
I've not tried either on any smooth leather everyday boots yet. I too have used it for years on my smooth leather hiking boots. I never noticed a visible change in the leather on those boots, but I also wasn't really thinking about it.