It is neither of those in my experience with many different services on IFTTT. It is slow, very slow in fact at times, but I wouldn't equate that with reliability. When it's slow, it's consistently slow 
Sorry, but you cannot directly integrate ring at this time. There are workarounds
for motion and such. Ring is cloud, so expect that you will have a cloud solution no matter what.
Not sure I understand the comment about Google Assistant, since you want Ring to trigger an action on HE don't you?
