The FL-40 is one of the best flash units around. You could get a different flash unit and still use it with your E-10/E-20, but why? Paired with your Olympus E series cam, you get full-auto functions, so you don't have to worry about complicated settings. In some situations, you may want to go manual, but on most occasions, having the FL-40's auto capabilities is a definite plus.
Another reason to spend around $300 for this Flash, is the power. The throw of the flash covers a very wide range. In the digital world, you want to be as compact as possible, especially if you are mobile, and do not want to carry around a lot of accessory equipment. The FL-40 is a very nice compact flash that packs a lot of power.
Below are some pics I took of a hockey practice with the FL-40 and without. The first photo is without the FL-40, about 50-70 feet away, at 1/60sec, in "S" mode. The second shot is with the FL-40, at 1/640sec, 50-70 feet away, in "S" mode. See the difference? The FL-40 can throw light very far.
If you own an E camera, you can't miss out on all the fun and great photos of this accessory.