I think that what we're looking for is the simplest solution to a problem. If you recommend a device that's been made to solve the problem, and you think that it's the simplest solution, then that's perfectly okay.
I feel like if we didn't allow people to suggest devices that actually solved problems, then it would just be a competition of finding the most convoluted way to avoid using already made devices. If the lifehack is more work than the product that it's trying to avoid, then it isn't a lifehack.
Now to fit in with what the definition of a lifehack is supposed to be. Since the most commonly accepted solution isn't really a hack, it should be important to note if the simplest solution isn't a hack.
An example of this would be if a person asked how to peel an orange. The common solution would be using an orange peeler. There might be other methods, but if using an orange peeler is the simplest method, then it can simply be noted in the answer that there is no lifehack for peeling an orange, and using an orange peeler is the best method. Then, ideally, the answer would continue to share the other methods anyways, for the sake of providing the most complete answer possible, and avoiding a mess of multiple short answers.