Anyone have any information about those food?
I saw some in petco and other pet store around my area.
The food that last in the sink for around 3-14 days, so u can be away and your fish will still have something to eat.

something like this http://www.petco.com/product/3022/Wardley-Vacation-Food.aspx
is there any dangerous about this?
if not, then I can use that even if im not away?

Those vacation feeders are notorius for mucking up the water quality. If they aren't completely consumed the food starts to rot (which is never good) and then theres the plaster being released into the water, if you're going to be gone a week or less they're not worth it. Even if you're going to be gone more than a week you should try all other options before thinking about using them. I used one once when I was gone for a week and a half. I used a 3 day one so I knew that it would all get eaten in a few days and then the fish would be fine until I got back. I wouldn't use it again though unless there were no other options, too much risk.