https://streamable.com/ndl2d2

https://streamable.com//65r0oi

https://ibb.co/2hjyrgF

https://ibb.co/st05Xqh

I got a new bike in March with Ultegra on it. After a few hundred miles, I was thinking the teeth look a little chewed up too even though I've been very aware of the shaping and sculpting they do on the individual teeth. It actually did look a little chewed up. Might have been me getting used to the speed at which the Di2 shifted and coordinating when I eased up a bit on the power. Certainly never noticed such on my previous 105 5800 equipped bike.

However I didn't worry... at least not much... and continued to ride the bike since it wasn't causing any issues. I did do some tweaking of adjustments, but that was more for noise and getting the Di2 lined up better with the sprockets.

Over 2000 miles (3218.7 km) later, it's still not an issue. The teeth don't look any worse and it shifts great.

One vid showed you pulling the chain to show slack while on the chain wheel. All I can say to that is measure your chain. A steel tape or metal scale works best for me. Just see how 12 inches compares to 12 links. If that 12th link is more than a 1/16th" beyond the 12" mark, then it's about time to replace the chain. If you are metric, then use 10 links and 254 mm, if beyond 255 mm then it's time to start thinking about it.

I keep a little tension on my chain with the crank and the rear on the ground or brake set. Then measure from left side of a pin to the same side of the pin near the 12" mark. https://road.cc/content/feature/when...-219450?page=1

11 speed and up, most say replace if 1/16" or 1 mm longer, roughly .5%. For 10 speed and lower some say you can wait till .75%. However it's up to you. I've had chains go twice that when I wasn't checking regularly and not had issues with new chain on cogs, but other times I have had issues.