So, as I understand this, you are planning to buy a carseat as a gift for the parents of your new grandbaby? Sounds great, and of course the parents' opinions are the really important ones.
That said, huge fan of the bucket seat. We had 2 parents + 1 grandparent driving baby around, not necessarily always the same for all legs of a trip (e.g. I would drop son at grandma's, grandma might run errands with him while she had him with her, then dad would pick son up from grandma's). So -- 3 bases, 1 seat, way easier and more affordable, in our experience.
And yes, we moved baby around in the seat <i>all the time</i>, asleep or awake. And no, I wouldn't have put him in a room by himself asleep in the seat, but I sure didn't hesitate to get him out of the car in the seat and let him sleep while we ate dinner (with an eye on him) or whatever. Maybe that wasn't sensible, but it is what we did.
I was a tremendously enthusiastic baby carrier, wore my son up through the point where he was 40 lbs & 3 years old (on my hip in a sling at that point), but I also used the carseat to cart him around, and definitely in grocery carts & such (in the younger part of this window, obviously). And while I wore him a lot, my husband had zero interest in baby wearing though he & our son walked miles & miles & miles in the stroller that came with (and would accommodate, though it didn't require, our carseat. My mom also wasn't into babywearing as a grandma, though she had been as a mom. So ... yeah. Huge fan of the bucket-style snap in seats.