No litter, no box, no clean-up
training (difficult and time consuming), cat falling in ? (gets scared and refuses to use)?, flushing (not that big of a deal), cat on toilet seat (personal hygene), might have to wait for cat if he/she is using it.
Over all it is very unnatural for a cat to use the toilet. If the cat is frightened of water then it will be difficult to train. A cat also needs to learn to balance. One big thing a cat must learn if expected to use a toilet, is not to bury. They will have nothing to bury it with. The biggest plus, is that it will save money. You won't have to buy litter, or liners (if you use them) you don't have to have a box either. It will save space that way. It is up to you and the reason you want to train it. If you want space/money saved, it is right. If you are looking for it to be less to deal with, it may not be. Not olny does training it take a very long time, but with the bacteria on the cat's feet, you will have to clean more often. It is up to you but hopefully this helped.