Generally there is a difference between clones and counterfeits at least in my books. Clones are sold as clones and might even have differences In markings. And cheaper price then the real thing.
Counterfeits are usually sold as the real thing and same price. And cheaply made in most cases. Check serial number if your buying a higher priced mod from a place you don't trust. Iv come across counterfeit tanks, coilheads,mods,batteries.
As for dangers read some reviews on the maker of the clone if it says who made it, if no one says anything bad it should be fine . A quick search will help you allot when searching for a mod.