It's just something everyone should be aware of.
It's up to you to decide if it's okay that you send a server provider (in this case late.sh) a bunch of your public keys which he could for example use to probe other servers to see if you have access to them.
Everyone has different opsec.
The site does include a way to use a throwaway key and IIRC it was there last night too.
Based on what another user said, you might want to modify the above command to use throwawayUsername@late.sh instead if you are going the throwaway route to be more certain you aren't leaking your OS username.