Tube bird feeders are given this name for the obvious reason; they are a tube shaped bird feeder that makes use of this unique design to offer a little something different to the birds that come to eat. The cylindrical shape makes it harder for a pest to latch on to it if they are going to try to steal seeds, or whatever it is you choose to feed, because they have nothing to grab onto. This means you lose less feed to the squirrels, chipmunks or other rodents who otherwise might see the bird feeder as a free meal. As well these kinds of feeders are more likely to bring you the smaller birds, so if you have a preference between smaller birds or larger birds that may be a deciding factor on whether you want this type of bird feeder or not.
Theses tube bird feeders can be a variety of sizes and so hold different amounts of food. But that is not why they attract the smaller birds as opposed to the larger ones. The reason for this is the size of the perches. These feeders tend to have perches up the sides of the tube which allow the birds to eat at different levels on the feeders. This is unlike the platform bird feeders where they all eat on the tray at the bottom. With these there is a tray to catch falling seed, but the birds can eat while sitting on a perch anywhere on the feeder. This means that you must keep the bird feeder full to allow the perches to be useful places for them to eat from. They can also eat from the tray, which may allow for some larger birds to hop on, but as very little will fall it is better to count on this type of bird feeder being for smaller birds.
Therefore if this is the type of bird feeder you want to use you will need to understand that you will not be seeing any jays, doves, cardinals, grackles or other large birds eating from it. If on the other hand you like chickadees, finches or nuthatches then you will be happy with this feeder. Tube bird feeders can hold a variety of birdseeds from the small Niger seeds to the much larger sunflower seeds. Check before you make your purchase because some will come with different sized holes for the use of certain types of seeds. You will also need to know what the birds in your area prefer to eat.