I grew up in Alsace (France) which is geographically and culturally close to Germany. Definitely Yekke land. I only heard about Sargeness as a child.
For what I can remember it is mostly the same: a while long fabric robe with a belt and long sleeves which is a reminder or the burial shrouds (or maybe the actual burial shrouds that will be used after 120 years, to be checked).
The sargeness I knew where made of a thicker material and with more lace than the kittel I know. But that might be because they were not made in China and sold for 20 shekel in Mea Shearim.
This http://catalogue.mahj.org/collec.php?q=1&o=16 photo is from the collections the Paris Jewish Museum. It does not quite look like what I remember but it might just mean my father was wearing a different type.