Upside-down bottles have not given me the improvement in performance that I was promised. I have so far attempted both ketchup and shampoo (different products).
#1: portion control is difficult. The bottles make you want to hold them perfectly vertically, but then the gravity assisted squirt may be larger than desired, or depending on the product consistency -- I'm looking at you shampoo -- you may come out in an unending thin stream, as I helplessly watch. If the bottle is oriented more horizontally, greater control is effected; however, this comes at the cost of product being smeared all along the dispensing end. Which leads me to
#2: mess. I can deal with a tiny crust of dried ketchip in the dispensing end of the standard upright ketchup bottle. However, being greeted by a crusty landscape in the upside-down bottle makes me despair. And woe betide the showerer who does not tightly snap the shampoo lid back in place, for the contents will ooze imperceptibly, until the lid is now wetly glued together with product.
#3: ineluctible ketchup water. Yes, ketchup is a tricky and non-Newtonian fluid. We've all known the anguish of that first squirt of what we hope is a tasty condiment, only to find that our hamburger bun has become sodden by as much as two or three cubic centimeters of thin, ketchup water. With practice, one can shake up an upright bottle of ketchup, and at least partially obviate this tomato-y catastrophe. I had hopes that the upside-down ketchup bottle would completely eliminate ketchup water, but alas! The truth is that some thixotropic gremlin sees to it that ketchup water is invariably waiting for you in the first squirt. And there is nothing that can be done about it! It's locked in place, waiting to torment you, immune to reconstitution through shaking.
#4: the endgame. We all know the trials and tribulations of getting the last shampoo or ketchup out of an upright bottle. Often we will use gravity as our friend and store the bottle in an inverted position, so that the product is closer to the dispensing end -- simultaneously providing the upside-down bottle with its raison d'être. And this inversion is often annoying, inasmuch as upright bottles are thinner at the top than at the bottom, making them impossible to balance upside-down. And yet this narrowing offers a profound boon than had not yet impressed itself upon my ratiocinative faculties. It usefully channels the product toward the nozzle. In the case of the upside-down bottle, however, its structural stability requires that it be wide on the bottom. Hence, when nearing the end of its utility, the interior of the bottle's business end is covered in a thin, but wide, layer of product. Upon squishing, it farts out a measly, diarrhœtic splatter, while the majority of the remaining product rests, quite provokingly, in an unmoving annulus centered on the now entirely unobstructed airway connecting outside and inside of the bottle. Angry shaking of the contents to again obstruct the airway produces ever diminishing, but ever more flatulent, returns.