I don't see why you think you need to buy a Pro version. The Free version should be fine for simple gaming; the Pro version is for commercial users...
https://secure.logmein.com/products/hamachi2/Calling your ISP to request bridged mode is a good idea, and the performance of port forwarding is normally better than the performance of a tunnel or VPN.
However, it may take them some time to get around to doing that. It can also cost you something to have your ISP make configuration changes, or they might refuse to do it altogether.
Don't assume your ISP will automatically be willing to do what you need.
However it will certainly help if you can tell them you have an Xbox and your own router, you want them to bridge to, and they (hopefully) won't want you to pay extra per month for an extra IP or extra modem to connect the Xbox with
