This is correct. If the firms in a cartel are quite certain about market development, they can agree on prices and the price development. If markets are very unpredictable it can be that firms are better off choosing different prices and to deviate from the price set by the cartel.
This is true. When products are very homogenous then the firms in a cartel can agree on just one price which is easier to control than several prices (cartels are also easier to sustain).