We have used the Gen 3 with the only issue being the gears failed, which when it happened August replaced the lock. We loved it.
We purchased the new Gen 4 when it first came out so we wouldn't require the bridge any longer, and have had significant issue since the beginning. 
We got locked out of our house for an hour as we didn't have our keys and the lock didn't work - friends with a spare key had to come to let us in. 
After weeks of Support assistance, the lock still didn't function correctly, and August replaced it. 
However, the new lock experiences the same issues - we cannot rely on it opening the door, via any of the August app, HomeKit, Apple Watch August app, or Siri. It cannot seem to find the lock. It Auto locks, but doesn't Auto Unlock or Unlock when requested. 
We've tried everything, but find we must use our keys more often than not as the lock cannot be found, by August nor HomeKit/Siri.