Well, in FFXI personal chocobos:
1) had to be raised from egg to adulthood before riding (took about a month i think)
2) personal chocobos were often times slower than rental chocobos.
3) personal chocobos sometimes had a shorter riding duration than rentals.
4) If you wanted faster and or longer riding time chocobos you had to breed several generations to fine tune atributes. (this could take months)

Now I'm not saying FFXIV chocobos will be the same as FFXI chocobos. But I'll as far to say Personal vs Rental there will be either speed or riding time will be reduced compared to rentals.

Or there is going to be a terrible cool down timer between calling for a ride like 1 ride per 36 hours



j/k j/k