I have both and though they are similar, almost exactly the same, I prefer Iris because she somehow feels more substantial. Elise, sad to say, feels too lightweight to me.
I have no idea what makes them different in that regard, just that they are.
We've had the Elise for some time and we're not all that impressed - but my wife recently got very interested in internal vibrators. The Elise used on the highest power internally does a very good job of g-spot stimulation.
I broke down and decided on the Iris but the Elise is probably the "classier" looking of the two but I like the Iris for the slightly more textured design.
If reviewers who have use both say they are that similar...save yourself some money and buy the less expensive one, unless of course there are discrepancies on how long they actually continue to work.