It won't protect you against someone being directly malicious, but it will against MitM, website hacks, etc. It also establishes semi-permanent trust on first use.
Your grandma is pretty advanced.
Grandma level: Grace Hopper.
But if the software is already installed, trusted package author also allows secure updates.
I also agree on the bad sides of the "curl pipe sh" pattern. Ideally, that command would be "apt-get install shellshare && shellshare", but haven't been able to write packages for it yet. There're 2 open issues about this: https://github.com/vitorbaptista/shellshare/issues/28 and https://github.com/vitorbaptista/shellshare/issues/31, if you or anyone else have some time to contribute.
So if you are going to use hashpipe, I think you should download it in source form, read it -- it's under 100 SLOC -- and then build it from source yourself. This way, you do that once and then in the future provided that you trust those sending you various scripts and binaries and the channel they used to provide the hash, all is well and no further manual verification is needed on your side of things ever again for any of those.
Beyond that, there's a simple matter of advertising: "Share your terminal (read-only)" may mislead some people about what is happening. A more accurate description would be "Give us control of your terminal (we promise we'll only let other people read it, not write anything)".
The only thing sent to shellshare's servers is the text in your bash terminal. There's no return channel for the servers to send commands back to the computer.
You could argue that you're giving control of the terminal because you're running a third-party executable, but that's the same for any executable you run.
Please don't tell people to do this. This is an idiom called "curl pipe sh"; you're asking people to run whatever code someone on their network decides to send them.
As an absolute minimum, you should change that http to https, so that they're merely running whatever code YOU decide to send them; but even that doesn't quite fit with the "share your terminal (read-only)" philosophy...