Is it a pannier or is it a rucksack? The first thing you notice about the Ortlieb Vario, aside from its Ninja friendly good looks (it does come in two colours other than post-industrial mat black- red/black or lime green/black) is that it’s got all sorts of complicated looking bits and pieces attached to it.
Where most seatpacks are fabric-based affairs, the Ortlief Mudracer has a thermoformed semi-hard shell to keep out the elements. If you've got stuff you need to take on a ride, and you need to keep it dry this is the seatpack for you.
The Mudpack's weather protection starts with a full zip protected by a silicon rubber flap which pulls down to keep water and debris out. Inside there's a zippered pocket at the top that's just big enough for a phone, and a soft padded main compartment that'll swallow a spare tube, a basic toolkit and some energy bars.
Ortlieb's TIZIP closure is the standard setter in waterproofing, and you could chuck this messenger bag in the river and still have dry clothes for work. There's ports for adding such extras as a sternum strap (one is supplied and you'll need it, as the bag is slippery) and inside there's, well, space for stuff.