The last Fusion5 $49 tablet tested in this video looks like it has the best performance. It maybe good enough for most average tasks like social networking, basic gaming, and web browsing.
The first two tablets look like they are good for using for reading short ebooks, playing very simple games like Solitaire or Chess, Twitter, and watching standard definition video stored on a SD card. But, maybe bad for watching online video if the tablets have slow Wi-Fi adapters.
I feel going to an offline store to buy a very cheap tablet is a better place to buy cheap tablets which are more likely to be low quality, and slower. Sometimes customers can test out the tablet before they decide to buy it, and ask the store staff questions about the tablet's performance and reliability. You can also return it at your local store if it breaks after a few days of using it.