Yesterday I took the ER9 groupset on it's first ride doing a quick 40km and 600m of climbing. I took it up and down one of the worst road climbs in our city with lots of pot holes, dirt and loose rocks. My aim was to see if I could drop the chain while constantly shifting the ER9 using the whole gear range. The ride included flats, climbing and fast downhill descents. The ER9 worked amazingly well! Shifting was smooth, my cables stayed in-place, I never dropped the chain especially on the fast bumpy downhill and I was totally satisfied with the performance.
There were only a few issues I had when riding. I seemed to accidentally hit the left shift button inadvertently switching to the small chainring while descending in the drops. Also I didn't like that both left FD buttons functioned the same. I'd prefer to have one button dedicated to the small chainring and the other to the big chainring. Without auto trim, it's hard to hear if the chain is rubbing on the FD or not especially when listening to music. The LTwoo grips are a bit too narrow for my taste, I tend to prefer beefier grips. The LTwoo hydro brake calipers work fine, but they're definitely heavy, I might swap them out later on for some lightweight calipers.
Also I think 12 speed is worth switching over to if you plan on buying this groupset. I'm not sure if the smoothness of my ride was attributed to electronic shifting, the wider range cassette, a freshly waxed chain or all of the above? Either way I liked I was able to keep a similar cog range as my 11 speed 11-32t and get the added benefit of the 34t in the low gear.
In regards to gearing I think 50-34t is as big as you can go with an 11-34t cassette with the ER9 without compromising shift performance. It can shift 52-36t + 11-34t, but without a clutch or some sort of cage stiffness adjustment, it feels a bit sloppy. Regarding battery life with lots of shifting due to up and down terrain, I was at 84% from full charge after the ride. I think it'll be a good idea to buy an additional charging cable as backup and maybe bring a power bank if planning a century or more. Also I'm not sure how long the CR2032 batteries will last in the shifters? I think I'll have to pack a few batteries in my saddle bag and dedicated screwdriver moving forward.
Overall my first impressions of the ER9 is very positive. With tax and shipping the whole thing cost me $350 USD for the groupset and it seems the early production kinks have been ironed out (crossing fingers). Also the money saved going with the ER9 can be applied cutting weight elsewhere like a lightweight cassette (which I opted for) or lightweight brake calipers. I still think it's a good idea to have a firm grasp of tuning a mechanical groupset. I don't think I'd jump straight into electronic without knowing how to tune a mechanical bike.