I have done a lot of ozonolysis reaction, its good to check the progress on TLC, the ozonide generally gives very slow staining with KMnO4, the alkene gives very fast staining. Some groups can react with ozone so it can be important to stop the reaction as soon as the alkene is consumed. Just keep the device in a fumehood. Also if any significant amount of ozone gets out the smell is very strong long before it is toxic.