I used to have the Pro addon when I when I was on ADSL and kept it when I transferred over to FTTC just out of sheer paranoia. After about 6 months having followed a couple of threads on here, I thought lets switch it off and see if there is any difference...
Can't say I have spotted a single difference with it off. Still hammer my connection just as hard, it has never effected online gameplay. Excellent ping times at all times. I've got 3 kids who will often be using Netflix/Spotify/Skype/Gaming whilst I'm trying to play Battlefield. Doesn't matter how hard I try to max my connection, I just can't spot any performance issues for the things that matter (which would be Battlefield, Skype, then all else !!)
Now I did have it when on ADSL because my line length/quality to the exchange was against me and I averaged around 2-3meg down, 200-300k up. That was probably helped by the pro-addon.
Given that I'm around 100-200M away from the new cabinet, that part of my line behaves pretty well and I now have so much 'capacity', any effect from the Pro Addon is lost in the ether..
As someone else has said, start without it and see how you get on, if you suspect bad performance, take a whole series of stats for a basemark, switch it on and see if you have any improvement.
Trust me, if I thought I got a single bit difference I'd been keeping it on after the ADSL connection I had but now I'm saving myself a £5 a month and couldn't tell you any downside performance wise..