Because people wrongly view preferreds as less safe than bonds, the preferreds tend to have better yields and lower conversion premiums. (The conversionpremium is the amount by which the price of a convertible exceeds the value of the common stock you would get if you converted.) Another plus: They are exchange traded, so preferreds are more liquid.
Most convertible securities allow the buyer to convert into common stock at a fixed conversion price set at a modest premium to wherever the common is trading at the time the convertible security is issued.
Not surprisingly iPads had better conversion rates than iPhones with a 42% premium, iPhones were very strong against Android phones with a 53% premium and iPods had a 28% premium over iPhones.