I am too looking for a good case for my new Mini 4. I have a SmartCase (real leather) for my Air 1. I was at first disappointed with the lack of a SmartCase for the Mini 4, so I tried the Apple Silicon Case and a SmartCover (expensive combo), thinking it's easy to return if things didn't work out. Well they worked much better than I expected, and I like this combo better than my SmartCase for the Air 1.
First, the SmartCase for the Air 1 is a really well made case, as minimal as one can get and still get pretty good protection. However, it still gets in the way of using the iPad. I do like the feel of leather better than bare sharp cold aluminum though, and that was the reason I got the case.
The Silicon Case and Smart Cover, while not leather, is nice to the touch, and is about as minimal as one can get. When folded behind the Silicon Case, the Smart Cover lies flat an is held one surprising well with strong magnets - it's like having no cover at all! This is one issue I had with the SmartCase. And of course the cover comes off with no effort.
The combo is pricey, but I think you really get what you pay for. I don't mind paying a little extra to have things work out as well as this combo. I can't stand those cases that treat the iPad like a yellow notepad inside a binder. I think aesthetically it's not very pleasing.