I see this is compatible with the Raspberry PI 3 B+. Is it compatible with the B also?

Yes, the monitor is compatible with the Raspberry Pi 3 B.

Questions & Answers: For Raspberry Pi 4 Touchscreen Monitor 5 inch HDMI Monitor Display 800x480 Compatible with Raspberry Pi 4 3B+ 3B 2B BB Black Banana Pi Windows 10 8 7

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For Raspberry Pi 4 Touchscreen Monitor 5 inch HDMI Monitor Display 800x480 Compatible with Raspberry Pi 4 3B+ 3B 2B BB Black Banana Pi Windows 10 8 7

5 inch small HDMI monitor with 800x480 mini LCD screen. The touchscreen is USB capacitive touch control, free-driver, plug and play, micro USB interface for touch and power supply, HDMI interface for displaying.
The power button can be turn off to lower power consumption. Built-in OSD menu adjustment function (adjustable Contrast/ Brightness/Saturation, etc.) Support audio output.
Can be worked as a Raspberry Pi screen, compatible with the latest Raspberry Pi 4, 3 B+, BB Black, Banana Pi and other mainstream mini PC.
Can be used as a general-purpose small HDMI screen, connecting computers, TV boxes and game consoles.
Package includes: 5 inch touchscreen HDMI monitor x1, HDMI cable x1, Micro USB cable x1, DVDx1, copper screws pack (4pcs) x1