Don't know about the new one but the lag on my 5" Show is kind of bad. I have mine set up so that it displays cams based on event triggers. When the mailman comes to the door every day, by the time that it comes up and shows that cam he's already long gone. Some of that (maybe 5-10%) is related to processing the trigger but mostly it's getting the Show to pull up and display. That is, even if I call for the cam directly using "Alexa, show front door" from the time she says "OK" it takes about 10 full seconds to display. Doesn't sound like that long, but practically it is. Also while watching the cam as it's being displayed there's probably about another 10-20 second delay in what's shown vs what's happening in real time.
Not useless but not real great either. I have it on my desk and it (eventually) pops up so it's OK for knowing when I have a delivery and things like that. Maybe the new one might be faster if it has a better processor. Not sure that I'd buy one for that purpose unless I knew that it was significantly better. UI3 on a tablet is MUCH faster.