Can these bikes work? Sure they can. They might also meet your needs. I went through this same thing when buying my bike. It is my understanding that these bikes from big box stores are basically throw away bikes. Meaning when major components start to go bad it's not worth fixing. Someone can correct me if i am wrong on that. I decided to buy what some people (not on here) consider a "real" bike which is anything that is not from a big box store.
To try and keep it short these bike will go down the road and get you from point A to point B. How long will they last? I am not sure. I know there are pretty cheap options for better entry level bikes but i know you have a really strict budget so i won't go into that.
Hope this helps.....