The massive problem with most smart watches, including Pebbles, is that the glass screen sticks out above the bezel and body of the watch. Traditional watches, espectially ones meant to be worn(!), have largely had a bezel that is raised higher than the glass. This prevents most bumps or knocks (which happens to something strapped to the end of a flailing arm!) from reaching the glass. It seems to me a case of cosmetics over practicality. Before Pebble I had a Timex Datalink USB which was a rugged watch, but suffered from bespoke half-plastic straps and limited functionality compared bluetooth connections (although battery lasted a couple of years).
Gadgetwraps have some skins for Amazfit Bip but whilst they do go down the curved edge, they don't look like they reach right to each edge. Is it also possible the Bangle.js 2 has a millimetre bigger screen than Amazfit Bip? The gadgetwraps clear protector doesn't cover the screen quite as much as the photo on the website suggests. I've never actually seen a real Bip to know!
I'm less bothered about the case getting bumped and dented -- it's going to happen sometime or another (although the steel Pebbles were excellent, the never-made Pebble Time 2 would have been my final smartwatch... if they'd ever made them)!
A cracked/smashed screen is more of a problem though, so I think it's worth putting something on the screen to soften the blow just in case. Tempered glass is great for taking most an impact but that's not going to happen for a screen with a curved edge.
One word of warning with polishing screens with small scratches, the later Pebbles had a special anti-reflective coating which looked very obviously missing if you tried to polish out a scratch, I don't know if there's any coating on the Bangle.js 2, perhaps something to reduce fingerprints given it's a touch screen? Alternatively, I've found that some obvious looking scratches almost disappear when you put a soft (i.e. flexible) protector on top of it.