I'm seeing this more and more but have no idea what they're called. Refer to this pictu https://cdn.jetphotos.com/full/6/53013_1459261993.jpg
This was Stefan Langer's Libelle, it's got those black plastic(?) thing at the aileron and wing. So does this Cirrus: https://cdn.airplane-pictures.net/im.../14/975766.jpg

What are they called and do they help in performance? Would it be worth installing?