I used to buy Japanese made feeders, they work perfectly. But I cannot get these anymore because they only sell China made ones in Singapore nowadays!
If they work, the pellets should be released continuously day after day and time after time. So IMO there is no worry about pellets moulding or fouling up. It's only if they stop for some reason or other....then you need to worry about replacing the pellets if they have already been compromised! But if so, you should also send the feeder back to the lfs and ask for a replacement.