i have 2 in my 240L with cherries and amanos and so far i have not seen them eat a shrimp yet.
they are quite active and do chase each other around a bit. they like to chase their own species i believe.
I had 4 in a 160l and that seemed like a good amount - they hung around together most of the time. Never saw any agression. (EDIT - I have heard that keeping them singly can lead to agression.)
I kept them for about 4 years and they were voracious alage eaters throughout. Just my experience, I did feed sparingly.
They also like to chew on soft mosses as well. They don't finish them off, but they leave them looking stringy\tatty.
feel a bit safer now in getting some, ive been reading up about them and wow! there is alot fo confucion as to the correct c.siamensis! does anyone have any spare or know where i can get some true siamese algae eaters! other than these flying foxes or false siamese algae eaters!!
True SAE's have the black band extending right into their tail whereas the flase ones dont. its stops where the body meets the tail. i bought mine about a week and a half ago from my local MA. they had a tank with false ones in and a tank with the True's in. as long as you can tell the differance you will be fine. google for pictures and you will see the differance.
I was also quite nervous about accidentally getting false ones. I also got mine from an MA that had the true and false ones in! Most LFS know the difference and I have never seen a false one labelled as a a real one.