I have two flying foxes--one is male and one is female. They are very fertile and I can count on a bunch of "babies" every 20-21 days. Unfortunately, they also eat their young. They are very territorial and have managed to kill off just about every fish in my tank. They are hiders and fun to watch. Since they are the only fish in my tank now, I have been able to observe their odd behavior. I like them, but would recommend that you keep them with faster and medium aggressive fish.
The only Flying Fox I ever owned died recently after nearly six years, three home moves of my own, and a move from a 100 liter community tank to a 250 liter one. This one also survived a power outage and resulting 12°C water temperature in one apartment and a heater malfunction resulting in 36°C water in another mishap during its life span. Thus, I think it's safe to say that this is an extremely durable, low maintenance fish that can tolerate a wide range of temperatures and conditions. Although it did "dart" from place to place, it was by and large a pretty lazy fish, eating only shrimp pellets and resting its swollen belly on the leaves of a giant Anubias or Amazon Sword in my tank. I don't believe it ever ate any algae past the first month. Though territorial towards several Praecox Rainbows (with whom it would compete for shrimp pellets), it seemed to get along with the remainder of its tankmates, probably because it was too slow and too fat to cause any harm. Coincidentally, I purchased a Siamese Algae Eater to replace it and as Jan has pointed out, the SAE has been much more diligent about eating algae in just two months than the Flying Fox ever was in its entire lifetime. I wouldn't recommend getting more than one and I wouldn't recommend keeping one in a tank smaller than 100 liters, but it will definitely grow on you if only for its durability and its longevity.
My experience disagrees with some of the things said about the flying fox. I've had mine for about 2 and a half years and he's been no trouble at all. He certainly doesn't eat the algae though. I find that he loves to rest on a piece of bogwood with java fern rooted into it. He spends most of his day grazing off of it.
I have had my flying fox since July of 1994, making him just over 9 years old. Reading the other comments here I think I must have a very docile one, as I have never had any trouble with him being overly aggressive. He gets a little ratty at times, but has lived for most of his life with a rainbow shark and various miniature cats over the years (the rainbow is almost as old as the fox, but not quite) and not managed to kill anything off. I do find him lazy with the algae, so had to resort to other bottom feeders to keep on top of things. He now cohabits peacefully with a couple of otos. I think they are beneath his notice though! My fox has also survived many a mishap with heaters and filtration and a brush with the dog! It made a bid for freedom through a gap in the hood during cleaning and was found about 20 minutes later being washed by my sheltie. The fish was stiff and had no sign of movement, mouth or gill and I thought it was a goner! I chucked it back in the tank, just to be sure, where it sank like a stone! About an hour later I saw it twitch, then it was off and running again. It earned its name of Captain Scarlet that day! Great fish, great personality, and if it can survive me, then anyone can keep it successfully!
We have 4 Flying Fox sharks in an 864 litre tank who swim in a pack and are not territorial at all. They live in a community tank with mollies, swordtails, tetras of all kinds, bristlenose catfish and many more. They are quite content to pick at any new shoot on the plants or just sit motionless on the leaves. They are a very interesting fish to watch.
I have lost 2 red tailed black sharks to this fish, plus a small corydoras. I currently have a bronze corydoras in isolation, as well as three silver sharks, which have absolutely been battered by this fish. Although it is beautiful to look at, it does unfortunately turn aggressive. Mine is now 2 years old and some 12 cm in length. It is also going back to the shop this week, before it starts shredding the Plec!