That will choke if you put more than one item in the dropper at a time (say, if there's hoppers coming in from two different sides, for example, or if you place some items in the dropper manually.) It will fire once, when the signal turns on, but then the signal will stay on since there's still another item in the dropper; it won't turn off and then back on again to fire it a second time. Instead, you can run a signal into the hopper like this, to make a clock (you'll also need another repeater, to point the signal into the dropper instead of just pointing back into itself):
Or, again, like lazyrunner said, you could remove the (first) repeater to make it faster, but it will always leave some items in the dropper, since it will stop firing once the signal gets too weak to reach the end. Also, you need to set the comparator to subtraction mode (right-click it once) if you do it this way:
(Also with this second one, once the dropper stops firing, the clock will keep running anyway, since the power does still reach that far. This may or may not be a deal-breaker, depending on your situation.)
However, in this, you'll need 41 items (items that stack up to 64, those that stack to 16 and those that doesn't stack counts differently) in the Dropper first. When you have 42 in the Dropper, it will then shoot out 2 items with a 1 tick interval. The Comparator makes a clock to make sure that the Dropper will keep shooting items.
If you however do not want to have items stay in the Dropper, you need to sacrifice speed (items will now shoot with 2 tick interval) and you'll have to use another Repeater. This is how I would do it: