The A4 is next in the lineage of the Prodigy "Approach" series. We are still waiting on description of flight characterisics, but it looks as if the A4 will be the straightest flying of the "A" series to date. The A4 does feature a truly unique "notched" rim, unlike any other disc currently on the market.
The 400G series is the regular 400 plastic with a shot of adrenaline. It is the base 400 plastic mixed with another resin that give the plastic a slightly different feel than the base 400 series. The additive also makes the disc more durable and requires more time to break it in.