The IKO Trade Top Sheet is a 2 layer system which is primarily designed for use on flat roofs; applied using cold bitumen adhesives (although the underlay can be nail fixed).
The IKO Super shed Felt is a single layer system which is designed for use on pitched roofs (20 degrees and above); this system has a much stronger polyester base (as oppose to the ‘rag fibre’ base used on the IKO Trade Top Sheet) which makes it ideal for fixing with nails on pitched roofs. Although this system only uses a single layer as oppose to two, because it is for use on a pitched roof it is less likely to be subject to the likes of moss growth, standing water etc. that may occur on a flat roof.
I hope this helps to clarify the differences between the two.