Using a 24VAC 10VA transformer which Eufy manufacturer instructions recommends for the E340 is not powerful enough, I had mine hardwired for 8 months with endless notification issues, Eufy did send out a replacement, still the same issues.
I have now purchased a 24VAC 30VA continuous supply transformer, now works flawlessly so beware before you hardwire the doorbell.
What kind of notification issues did you have?
Once the doorbell pressed, notifications stopped, so really a doorbell, no security. Hope that helps.