I would say that the manufacturer has a point about the actual application for which the product was made: a piece of electronics will retain much less water than a sponge, so providing a package that will absorb a ton of moisture is overkill. You had 16 times as much rice as you had of the desiccant pellets, and that extra mass provided at least 3.5 times as much absorption after three days (and three times as much after two days). The pellets would seem to be more efficient. A few other tests might be of value.
The first is to adjust the quantity of water involved. Find a broken (or breakable) device, weigh it, drop it in a bowl of water for a few minutes, shake it to get rid of the collected puddles, and then weight it again. How much water will tag along will depend on the device, but a test or two like this would give a good measure of how much water might be left to remove. Then you could re-run your sponge test to see how the two stack up and if the Bheestie Bag can eliminate the critical moisture in a timely fashion. The one possible wrinkle here is that the way the sponge is trapping moisture may not be the best parallel for how a device like a cell phone holds water.
Another test would be to try to create a rice-based equivalent to the Bheestie Bag: put around four to eight ounces of rice in a porous bag (maybe thin cloth or even the foot from some panty hose) and toss that into a zip-lock bag. If the rice can still absorb a useful amount of moisture while in the porous bag, then you avoid the one big pitfall of rice: getting it stuck in the device. It may be that a DIY package like that (with rice as the desiccant) could do a satisfactory job. It may also be, however, that rice isn't efficient enough a desiccant and doesn't get the moisture out as effectively when deprived of that "stuck in all the inner workings" contact or reduced to such a small quantity.
Of course, the best test would be to do all of the above and determine the optimal DIY solution, then take two actual devices and throw them in the drink.
