If the tyre pressure is kept high unicycles are not prone to punctures. Snake bites are common if the unicycle is ridden with the pressure too low.
Blow-outs are common with worn tyres. It is always useful to have a spare available. The manufacturer will vary depending on availability.
All have Schrader valves which are of higher quality and are more appropriate due to their ability to withstand high pressure than "woods" valves as supplied as standard on many unicycles.
These innertubes are the ones that are fitted to the Nimbus, Onza and Kris Holm trials unicycles as standard. Please note that although they are specified at 20"x2.125, these are the largest tubes available and recommended by the manufacturers of the 19" trials tyres.