A quick Google search of "site:
www.zen-cart.com Fantastico Problems" will show you 182 reported problems. No telling how many went unreported. Fantastico is often manipulated by the host and seldom installs a truly correct/complete Zen Cart Version.
As to local development... Unless you possess a direct 20Mbp pipe to the host, you can see and do everything locally, instantly, and without bots getting bad information that will turn off a customer.
If you are able to turn off prying eyes and don't mind the delays and possible FTP glitches, go for it online.