The only initial downside I'd say is that Indian style basmati rice ie each grain seperate isn't what is produced. But now we've tried the cooker version - but we now prefer it because it brings out the fragrance of basmati to a degree we haven't seen before, and the basmati produced seems designed to absorb curry sauces rather than be eaten alongside.
There are a few ways to get separate grains with rice cookers. The best method I've found so far is to use 2/3 of the water called for in the recipe and then when the cooker says it's done, I switch it to manual/slow cooker/steamer mode and add the remaining water and finish cooking the rice with the accessory lid. That way you still get the fragrance and a bit more of the fluffy texture. Experimenting a few times will help you figure out the approximate ratios and times for the texture of rice you're after.
An alternate way is to let the cooked basmati dry out by increasing the holding time after cooking, or by holding with the lid partially propped open with the paddle.
No matter what style of rice you're making or style of pot you're using, the trick is to open the lid as soon as the rice is done to release the extra steam and fluff the rice in the pot immediately. Keeping warm always comes after fluffing.