I got the HooToo USB-C Hub Amazon 
(Model HT-UC008) for Christmas. This hub does not have a pass thru USB-C power port, any power the hub uses is drawn from the computer, which in my case is the Google Pixelbook.
First thing that I did was plug in the dongle for my Logitech keyboard and mouse. While I am not using the Logitech keyboard right now, I am using the mouse. Both keyboard and mouse work as expected.
Next I plugged in a HDMI cable to connect the Pixelbook to my HP S240ml monitor. Chrome OS correctly identified the monitor and defaults to extended display.
The display extension assumes that the Pixelbook's display is to the left and the monitor to the right, but I have the Pixelbook in front so I arranged the display extension to that configuration using Settings, Device Displays.
The Chrome OS options for the HP S240ml include changing display size, ranging from tiny to huge, the resolution, orientation, and overscan. The resolution defaulted to the max 1920 x 1080 (60 Hertz) that the S240ml supports.
The hub comes with a SD card slot, so plugged in a 512MB Sandisk Ultra card, which Chrome OS recognized and suggested to open Files to see the contents on the card.
Files displays the SD card as a USB drive but it doesn't really show any files, just what appears to be a folder named System Volume Information and in that what looks like a file named IndexerVolumeGuid.
I ejected the card and inserted a Kingston 128 MB SD card. The card was also recognized and shows a My Documents folder with a file named Backup.pbf. The root folder also contains a file named ignore_my_docs that has 0 bytes. The card had a really tight fit.
I copied a jpeg file to the root folder and opened it to confirm it wrote correctly, which it did. I then moved the file to the My Documents folder and again confirmed it wrote correctly.
Next, I started Typora, which is a Linux app, created a test file, selected Save As and observed that the USB Drive does not appears as a destination for the file. I was able to copy the file to the SD card using Files. (Note: Looks like Crostini access to Chrome OS directories and USB devices won't be available until Chrome OS 73.)
For grins I also tried IAWriter, which is an Android app, and it doesn't really even have a Save As option. You can Export a file, and I selected Export Text and Files as a destination, but I have no idea where it ended up.
I inserted the Kingston card into the Macbook and it found both file, but Preview did not fully load the JPEG. I also wrote a text file to the Sandisk card.
I put the Sandisk back in to the hub and browse the directory where I wrote the text file and it displays in a browser tab. When I right-click the file and click Open With in Files, I see options to open in View (default), iA Writer (Android), Atom and Sublime Text (Linux) and Caret (Chrome OS).
When I open in iA Writer, the file stays in the Android file system. When I try Atom or Sublime text I see a message that says I must copy the file to the Linux file system first. Finally, when I opened the File with Caret I was able to writ back to the Sandisk card.
Final note on the Sandisk. To see the amount of available storage space I first click the USB Drive to select it, then click the Options menu (three vertical dots top right of the screen) and see that there is 482.7 MB available.
I inserted a Sandisk 64 GB USB drive in to the USB port of the hub and browsed its contents, which list as expected. I observed faster read/write time with the thumb drive.
I've been using the HooToo hub for a while now and I've discovered a problem with audio over HDMI. I've been keeping an HDMI cable plugged in to the hub and switch the HDMI port on my monitor to it when I plug the hub in to the Pixelbook.
Video consistently works as expected. Audio, however, frequently does not play. What I have been doing is disconnecting the hub from the Pixelbook, play the audio on the Pixelbook, and then plug the hub back in and that usually resolves the problem.