I tried it on one of my remaining plans and it worked fairly well. When I picked DB user it didn't accept my first name as there was already someone using that name, so I just added a few characters after it and it worked.
Later on when you configure the installation via the browser on Mambo itself, there's something in the email instructions re step 3:
-> Path : remove the ".blah" part.. it's not necessary!
I couldn't figure out what the .blah was supposed to correspond to, so I left it alone and the installation seems to be ok.
Not sure which plan is best? This chart lists the plans.