I've got STIs, bar-ends and downtube shifters on various bikes. They all work well, but STIs definitely make it easier to shift. The big advantage to bar-ends is that they are much less expensive than STIs and supposedly more durable and less prone to failure. However, I had some Dura-Ace bar-ends wear out with less than 3 years of use -- although fortunately still covered under warranty. Bar-ends are much easier to use than down-tube shifters and only marginally more inconvenient than STIs.