Overall they aren't hard to operate or maintain. Most are very durable, but there is a certain amount of upkeep you will need to perform to keep them going. When buying one of these be sure you plan your budget accordingly. Make sure you factor in things such as extra glow plugs, fuel, after run oil, etc. Also you need to know before you start that you will, at the very least, have to change the cylinder and piston at some point in the future.
Also be aware before you buy that you aren't going to be able to just switch it on, drop it on the ground and go like with an electric. Nitro's require a certain amount of patience.

As long as you have patience you will have a great time with a nitro car. They add a realism to r/c cars that electrics just can never get.