After 2 months with the U400...
I replaced my six year old Yale August lock (YRD226 with the HomeKit module) for an Aqara U400. I upgraded my home network to eero (from Orbi) two weeks ago and the August Connect wouldn't reconnect despite multiple resets.
Choice... I looked at a couple options but picked the U400 for the additional features (fingerprint, HomeKey, UWB) along with having a physical key and the rechargeable battery. I have been extremely happy with the Aqara G5 Pro camera and thought I would try the smart lock.
Install Process... The lock installation process went extremely smoothly and took about 25 minutes. The physical installation went well with no problems. I did re-use the Yale strike plate rather than replacing it with the Aqara provided components. One nice thing is the U400 was just slightly larger physically than the Yale so it complete covered the original door paint and scuff marks that were under the Yale. Calibration worked fine with no issues or adjustments.
I followed the QR code instructions. I already had the Aqara app and account so that sped things up. The U400 battery needed to be charged (it was less than 40% out of the box). It added to my network and I added it to Matter as well. All without problems. Configuring the users is a little different than Yale/August but I was able to add my code, fingerprint and my iPhone unlocks with a tap. My wife was a little more difficult adding her fingerprint, but switch to her thumb and it worked fine. I have not tried the UWB "on approach" features yet. One nice feature is the Notifications for the door lock can be configured to show the video from the G5 Pro.
Two months later.... I am very happy with the U400 in my primarily HomeKit environment. It is easy to add codes and fingerprints. I added the "unlock on approach" about a week ago for my iPhone/Apple Watch both works as expected. I have not tried to add unlock on approach for my wife or anyone else.
We had a house sitter here for a few days and she used the fingerprint reader to let herself in. It was quick to setup and worked flawlessly each time she used the lock.
On the battery side, the device reports 87% remaining in the Aqara app and 90% in the Apple Home app (an odd discrepancy). I am impressed with the battery life after two months, appreciate the battery meter and won't need AA batteries for the Yale.
Overall, very happy with my choice so far. I'll be looking into the Aqara doorbells shortly to replace an old Nest Hello.