With ANY online TA, don't expect much service. And yes they are most all the same. I book based on price only and need nothing more than a valid ticket. If you need more than book with an agent who can give it to you.
With ANY online booking, ALWAYS, get the cruiseline booking number and verify this YOURSELF directly with the cruiseline. Check your credit card charges as well.
I have been doing this for years and never had any problem. It can pay significantly to compare prices with several agents.