They can be used through glass if you put it really close but the manufacturer doesnt recommend it, it isn’t reliable if used this way ime.
Image wise I think they are pretty good, night time unlikely you’ll get many facial features, but you’ll definitely tell it’s a person and tell what they are up to. In daylight the images are pretty good.
Motion sensing and alerting is quicker and more reliable than the arlo HD system I returned, which costs lots more £££. I’ve now stumped up for a hard wired swann system on the outside of the house.
I use the clever dogs mostly as a peep hole in internal rooms, so if my alarm goes off, or I think I hear something I can check in or just want to check in remote. I also use one instead of a baby monitor for our toddler, the much more expensive baby monitor is in use for son#2.
They are only £25ish and amazon are pretty good with returns if it turns out to not be what you are looking for.