I'm curious to know what developers on the receiving end of these tools think - are they invasive? Are they useful? Does it feel weird being "watched" in this way?
Like any tool, a lot depends on how these metrics are used - and who's looking at them and making what kind of judgments.
I can see the value on some level as a means to potentially improve developer efficiency...but I'm curious to know how that actually plays out
It's kind of like how in a proper team where there is already trust and no micromanagement, everyone continues to do their work and remain productive no matter what, while often in a team where management does not care about ICs and treats them as disposable, and the they only show up for an income, are hourly, or just churn out crap in volume, they're gonna slack off as soon as your back is turned.
It entirely depends on their use, ask the team(s) involved first, and the level of trust. You'll be strung out to hang if your team already doesn't trust you and now you want to throw this "surveillance watchdog garbage" at them.
If your team trusts you as management, you may get some kind of buy-in as to how some graphs may help them work smarter, but at that point it's likely something they don't _need_, and if you start forcing value judgements off that data there's a high chance they're going to resent you for it.
If you have tools that use git to pull metrics to see who your "best" developers are, don't be surprised if developers create or use tools to optimize their changes for the metrics rather than add value to the codebase.