You won't notice the traffic management on BBYW pro at all. I used it for a few months before Christmas and performance is very good. Everything you would expect to work, just works.
The only problem I had with BBYW Pro was trying to stay in the 10GB usage allowance. I really struggled with this. I share my connection with 2 other people in the house and average usage comes in at around 10-15GB.
You don't need to seriously worry about the 10GB allowance unless like me you use external FTP fairly often as after you hit your usage cap this is blocked along with Usenet and P2P.
Gaming and general use all work fine though, even after use your up your allowance, just at the slow speed of 128Kbps until the end of the billing month or you buy more allowance.
A tip is if you can, leave a computer on overnight and schedule Windows Updates, Games Demo, or whatever to download between midnight and 8am as you get free usage then