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.
The quick release plate srews to the saddle rails and the pack feels nice and secure, and there's an extra Velcro strap to fix it to your seatpost. There's plenty of fore-aft adjustment too, which is a nice touch you don't always get.
It looks wide, but we didn't ever have any problems with the pack interfering with our pedalling. The LED rear light is stuck on rather than built in: It fixes through a hole in the shell and is powered by button cells. There are flashing and continuous modes but it's best as a secondary or emergency light because it's not super bright.
If you like riding in the wet, or routinely have to, then the Mudracer is a great place to stash your phone or other valuables away from the grip of the elements.
Ortlieb's big thing is usually weatherproofing, and that's the case again here - it's hard to see how the Mudracer could be any more waterproof than it is without using a hermetic zip. Oh, and without drilling a hole in the shell to fix the light through.
So long as the light is kept nice and snug it shouldn't be an issue, but unless you particularly want the extra light we'd suggest that the cheaper non-LED version is a better bet – the construction, not the light, is the best thing about this pack.