Define "level" please.
Shimano products are pretty durable, whereas the same size ****ese clones are usually made out of imitation steel that wears out faster. I've found sun clones are pretty durable.
One usually specs a sprocket cluster by # of teeth max and # of teeth min, + # of speeds. There are freewheels that screw on the axle and cassettes that are held on by an external retainer ring. I thought most 7 speed shimano parts were freewheels. At least the unnamed shimanos that come on discount store bikes are freewheels.
Note almost none of the vendors on e-bay amazon use the right description and most use both to get buyers needing both products. Half those buyers will have been defrauded.