Plasma cutters work by sending a pressurized gas, such as nitrogen, argon, or oxygen, through a small channel. In the center of this channel, you’ll find a negatively charged electrode. When you apply power to the negative electrode, and you touch the tip of the nozzle to the metal, the connection creates a circuit. A powerful spark is generated between the electrode and the metal. As the inert gas passes through the channel, the spark heats the gas until it reaches the fourth state of matter. This reaction creates a stream of directed plasma, approximately 30,000 F (16,649 C) and moving at 20,000 feet per second (6,096 m/sec), that reduces metal to molten slag.
Thats the explanation in technical terms.
I used them a lot in the past and they are very effective although I would say that 10mm plate is pretty thick for a portable unit due to power etc. If the unit is only just powerful enough you will probably get a lot of hardened slag at the edges of the cut . This will clean up but adds to the work effort.
How intricate is the piece as a metal band saw may do it, try some sheet metal shops in your area as they may do a test peice for you at not too much cost.
Hope that helps.