The TB20 is not a goldfish bowl. Most of the ceiling is opaque, and grey in colour. This is typical of most low wing planes. But sunshine is sunshine; it gets everywhere and sometimes - at high altitude - I struggle to keep the stuff out, so I have suction pad mounted sunshields (Halfords) on the side windows.
The Diamonds are different, as is a Tomahawk and a few others.
The construction of a "sunlight readable" LCD is not something I have yet sussed out but it is a kind of a normal LCD with several layers stuck on the front. The whole lot is polarised so that at the end you the the image but the reflections of incident light get dumped. Some salesman was telling me that if you peel off these layers, you don't see the image at all, which I found bizzare, but it may be true. The extra cost of all this is about £200 on most tablets which offer this as an option. I am certain that the G1000 and similar glass avionics use this technology too, although if you have unlimited power then you can achieve any desired contrast simply with a powerful backlight, and a darkened front layer.
There is a pile of superb tablets around now, but nearly all of them don't offer this option.
The I-Pad will sure find uses but it is IMHO grossly over-rated for European aviation. It has loads more applications in GA in the USA, due to the abundance of free material out there. If they did it with a decent display, it would be superb.