Recently I purchased this X100 expansion board for my Raspberry Pi, mainly for its HDMI to VGA output but the RS232 port was of interest assuming that it works as I expect it should!
The kit includes the following items 1x USB male-male adapter, 1x HDMI-HDMI male-male adaptor and mounting hardware to secure the expansion board to the Raspberry Pi. Also included is an optional reset switch pin header that isn't required for the board to function but adds the function to reset the Pi but this should be used only as a last resort because you face the strong possibility of corrupting the SDcard if you happened to drop the power while the SDcard is in the process of writing to the card!
Installation is pretty straight forward, there's two mounting posts and you line up the GPIO pins, then plug in the USB & HDMI adaptors and that's it! At this stage you have the option to solder the reset pin header to add that functionality if desired.
My thoughts, if you use the kernel that's available from Suptronics you have access to the RTC on the board, however this is a 3.6x kernel and is a little old. The drawback in using this kernel is that you would need to manually go through the setup process every time your Raspberry Pi had a kernel update, or you could just pin the current kernel you have to prevent this. There's also no source code for the modules that are provided with the kernel so you can't compile them to be used with a later kernel, if you don't really have a use for the RTC then not a big issue but after all if you purchase one of these you'd want to be able to use all of the functions! Although I'm sure that some searching should find either a newer based kernel or the ability to compile one (I've not checked as of the time of writing) Sure if I simply wanted a HDMI to VGA converting function I would have simply got something else that may have been cheaper.