There are even special litter boxes sold that are intended to go on the toilet seat for this type of training. But as cool as this is, I believe it can be dangerous, especially for owners of male cats.
Cats' urinary habits are important to keep an eye on. A change in urination volume or frequency can be the sign of a critical issue that requires veterinary attention. You just can't easily track urine volume if the cat is going to the toilet, even if they don't flush.
With a litterbox, you can get an idea of what their normal clump size is and notice if that changes. Regarding frequency, maybe you can hear your cat jump on the toilet, but I'm not sure it's as reliable as hearing them repeatedly scratching the litterbox. If you are out during the day and come home, with a litterbox you still notice the pee clumps to get an idea of how much they've peed - unlike with a toilet.
One aspect where the toilet may actually be better is that you _might_ be able to spot blood easier in the water.
I also wanted to train my first cat to use the toilet, until he suffered from a urinary blockage as a kitten. If he'd been using the toilet, I likely wouldn't have noticed that anything was wrong until it was far too late. Blockage is more likely in male cats, and it is _not_ an uncommon problem. It is already far too easy to not notice if a cat is blocked if you're not careful, and it doesn't take long at all to become life threatening. I believe a toilet would only exacerbate this risk.
If I see blood in the litter, no clumps, or clumps that are smaller than usual (or heck, even much bigger than usual), I know to pay extra attention to my cat and either book a vet appointment or go to the emergency room. It's allowed me to catch bouts of infection, crystals, and idiopathic cystitis early (all of which he is now more prone to after his initial urinary problems). A cat's kidneys and urinary system can also be impacted by stress levels, with unexplained straining and bladder inflammation thought to be in some cases caused by stress. Having them pee in a toilet in my opinion decreases visibility of a very important and sensitive health factor.
Cats' urinary habits are important to keep an eye on. A change in urination volume or frequency can be the sign of a critical issue that requires veterinary attention. You just can't easily track urine volume if the cat is going to the toilet, even if they don't flush.
With a litterbox, you can get an idea of what their normal clump size is and notice if that changes. Regarding frequency, maybe you can hear your cat jump on the toilet, but I'm not sure it's as reliable as hearing them repeatedly scratching the litterbox. If you are out during the day and come home, with a litterbox you still notice the pee clumps to get an idea of how much they've peed - unlike with a toilet.
One aspect where the toilet may actually be better is that you _might_ be able to spot blood easier in the water.
I also wanted to train my first cat to use the toilet, until he suffered from a urinary blockage as a kitten. If he'd been using the toilet, I likely wouldn't have noticed that anything was wrong until it was far too late. Blockage is more likely in male cats, and it is _not_ an uncommon problem. It is already far too easy to not notice if a cat is blocked if you're not careful, and it doesn't take long at all to become life threatening. I believe a toilet would only exacerbate this risk.
If I see blood in the litter, no clumps, or clumps that are smaller than usual (or heck, even much bigger than usual), I know to pay extra attention to my cat and either book a vet appointment or go to the emergency room. It's allowed me to catch bouts of infection, crystals, and idiopathic cystitis early (all of which he is now more prone to after his initial urinary problems). A cat's kidneys and urinary system can also be impacted by stress levels, with unexplained straining and bladder inflammation thought to be in some cases caused by stress. Having them pee in a toilet in my opinion decreases visibility of a very important and sensitive health factor.