The differences between the Tarp Ponchos come down to the fabric they're made of and the use to which they will be put.
The Nylon Tarp Poncho is perfectly adequate for recreational use. It is made of a 70 Denier nylon of much higher quality than 'basic' tarp ponchos and with better features (particularly the hood). It's a great choice for most hikers and backpackers.
The Ultra-Sil Nano Tarp Poncho is made of a 15 Denier siliconized/PU coated nylon which is an extremely high-tech (and thus high cost) fabric. It is significantly lighter (8.1oz / 230g compared to 14oz / 400g), and packs down to less than half the volume of the standard Nylon Tarp Poncho. The Ultra-Sil Nano Tarp Poncho would therefore be the choice of a consumer who intended to use a poncho/tarp combination on an extended, frequent basis - for instance, thru-hiking.