Advantages

   Maximum contrast lettering: the legends are bold and vibrant and pure in tone, with smooth edges and uniform colouration.
   Zero wear: the legend will never wear, as it runs right through the surface of the keycap.
   Colour freedom: the keycap and legend can each be of any colour desired: this lends itself well to custom keycaps where a wide range of colours is highly desirable.
   Feel: the legend and the keycap are one, and the legend cannot be felt while typing.

Disadvantages

   Cost and availability: the process of building moulds for each and every legend is an expensive process compared to making one mould per row profile and adding the legends afterwards on demand, especially considering manufacture for the wider international market where even simple letters such as "A" move between row profiles (e.g. QWERTY vs AZERTY, QWERTY vs QWERTZ).
   Single colour: typical double-shot processes restrict the keycap to a single legend colour, although it is possible to inject further colours and this has been done.
   Low resolution: double-shot legends are limited to low resolution designs with broad strokes and rounded corners. The range of typefaces and symbol designs available with pad printing and dye sublimation cannot be achieved with double-shot, as the moulding process doesn't support the fine detail and sharp edges that those processes afford.
   Gloss and yellowing: Double-shot moulded keys are made from ABS plastic because most other plastics shrink too much in the moulding process. ABS may yellow over time, and is not as hard as PBT plastic. The texture of PBT keycaps will remain longer than the texture of ABS keycaps - the ABS keycaps get glossy after extended usage. Because of this, PBT keys with dye sublimated legends are regarded by many as an even better alternative, although dye sublimation has its own set of disadvantages and limitations, most notably it cannot be used to print light legends on dark keycaps.