Despite the name, they are NOT plug compatible Raspberry Pi clones. They are great little devices though once you get familiar with them. They do require some decent linux skills to work with.
Most if not all of these boards require you to also buy an SD card (they say TF card, but I have had complete success with SanDisk microSD cards). You also will need a good 5 volt 2 amp power supply with the proper barrel jack. You cannot power these via USB. You should probably get a 5 volt 3 amp supply unless you get a really good 2 amp device. This will save your some heartache.
I should also point out that I never expect to connect an HDMI monitor, keyboard, and/or mouse to any of these. I work using the serial console or over the network using ssh. I view these as engines for embedded programming projects, not general purpose computers. This is not to say that you couldn't use them as general purpose computers, but that is not what I am doing, so don't expect any guidance from me; I have an X86 linux desktop for that.
I buy mine direct from Shenzhen Xunlong (from China) via AliExpress and have been completely satisfied doing that. This involves a wait of 2 to 3 weeks. This boards are starting to show up at places like Ebay and Amazon with shorter ship times (and higher prices).
At this point I am working with a pair of H3 based "PC" units and one H5 based "PC 2" unit.
Tom's electronics pages / email@example.com