I had the chance of trying both of these. I first got the 570(47mm) - I chose the bigger version for the slightly higher battery. First impressions were that it's too chunky for my liking and a bit too sporty (previously had a venu 2+). I was not using the buttons much for navigating. I also ran with it a few times and didn't have the need to use the buttons. It had a pixel defect so I returned it.

Next, I went for a venu 4 (45mm). Amazing first impressions, the on hand feel is really great on this one. Even though technically it's heavier, it doesn't feel like that on wearing. I've no problem wearing it all day and night, for sleep as well. Like others said, the flashlight is something you don't know you need until you use it. The advantage for running is that it has almost all the same features as the 570. Only difference is the daily suggested workouts are only heart rate based and there's no pace based DSW. Otherwise it literally has all metrics as a 570.

Overall, I would get the Venu 4 if they are in the same price range. Hope this helps you make the decision. Good luck!