EDIT:
Then I might be better off with the Anaiis USB stack and an clockport Subway from E3B for my A500s. I have clockports on the Viper520s fitted in my A500s.
This solution seems to offer both - keyboard and mouse support - and even more:
You might be better off, but the major disadvantage with a usb stack is that it's not compatible with anything that hits the hardware directly & devices don't work until you have run it. So if you boot a different disk or skip your startup sequence then you no longer have a keyboard (although you'll need to use a real amiga mouse or one that uses a separate usb adapter to get into the early startup). The boot problem could be sorted by burning a kickstart that supports it (although I don't know if this is currently possible), but that won't help software that bypasses the operating system. So games and demos and utilities that bypass the OS are still a problem.
The separate keyboard and mouse to usb adapters are the only safe way to go. The usb adapters that need a usb stack are more useful for storage/printer/network etc. A mouse isn't a major problem as you can easily have an amiga mouse plugged in at the same time, but having to have a backup amiga compatible keyboard is too much of an inconvenience.
I don't think there is a solution yet that allows legacy keyboard and mouse emulation as well as supporting a usb stack, this would be the ultimate solution and is the way the PC gets round the issue. In the mean time this is a good compromise.
This product exists purely because there is a need for it.