The data rate they specify is probably the signalling rate so halve it and take a little bit off to get your real transfer rate.
Also it's shared between everybody since everybody is on a single circuit.

It does depend on how much interference you've got on your mains wiring. It works great for some people but others don't have any luck with it. I've got a few dodgy SMPS's which generate enough interference to totally knock out any *-over-powerline technology. It also doesn't have to be within your house, any nearby house could be coupling back this crud onto the mains wiring outside.

It's easy but how reliable it is variable. If you must have reliability then go for wired ethernet. If you don't mind the possibility of outside interference then use wireless or powerline. I'd say wireless is more reliable as you're able to select different channels still.

Your best bet would be to try it and take it back if it doesn't work and also pray that nobody uses their arc welder nearby