A replacement seat cover for Miyata or Carbon fiber seats that allows a lot of extra room for padding. Available in vinyl or leather.
Strengths
Allows fitting a lot more padding than the standard Miyata seat cover in to the seat.
Weaknesses
The vinyl cover does rip if subjected to heavy abuse i.e. lots of drops.
The Gemcrest cover reviewed here doesn't allow quite as much padding as the Roach cover. Larger versions are due out which will allow even more padding though.
Overall
When you've spent a long time (or even a short time for that matter) in the saddle you'll come to realise that unicycle seats aren't really up for the job as far as comfort goes. By replacing the existing cover with one of these you can take full advantage of the extra room for padding. I've got a 20" inner tube in mine and the difference is amazing!
If MUni or trials riding is your thing then chances are your unicycle will see more forceful drops and bumps than most. So, if you're going to get one of these, I'd recommend paying the extra for the leather version as it's much tougher and will last a lot longer.