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Google Cloud Shell is a hosted development environment in Google Cloud Platform, consisting of a durable home directory, an ephemeral VM instance with the Google Cloud SDK and application default credentials pre-installed, and both a shell environment as well as an Eclipse Orion IDE instance, making it easy to develop for Cloud Platform.
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Pros
Pro VM is always up-to-date, making it more secure
Because the VM image is managed by Google and either provided entirely by Google or configured by a Dockerfile (which is regularly rebuilt), packages are far more likely to be kept up-to-date with the last patches and security fixes compared with Cloud IDEs that give you your own VM and make you, yourself, in charge of applying updates.
Pro Supports custom software packages via a Dockerfile configuring the Cloud Shell image
With Cloud Shell custom environments (an early access feature), it is possible to specify a "Dockerfile" to specify a custom VM image to use for the Cloud Shell environment. This Dockerfile can be used to install packages with apt-get, npm, pip, etc. globally.
Cons
Con Ephemeral Disk
Software installed globally as root (such as via "sudo apt-get install..." ) can be lost when restarting Cloud Shell; any software that needs to be persistent has to be installed in the user directory (or made part of the Docker image for the custom Cloud Shell image).