I just converted my factory BoV to FTA on my Flex today.
What does this do for you?
Nothing but making a PFFFFT noise when you lift the throttle under boost.
Is there any downsides to this?
No, the car is speed desnsity so releasing the air from the turbos to atmosphere when the blow off valves open does not negatively impact the tune, factory or modified.
BTW, I couldn't find 1" vacuum "nipples" to block off the factory tubing so I went to Home Depot and searched around, found some 1" rubber chair leg "tips" to use, worked pretty good so far.
Front Blow off Valve and blocked off tube

Another shot of the factory Blow off Valve with the return tube removed - vent to atmosphere

Close up of rear portion of intake tubing with blow off valve return hose removed and blocked off. For me easiest way to get to this area and remove tubing was to remove the intake tubing and rotate to access the clamp that held the tubing onto the blow off valve.

Rear Blow off Valve

Complete turbo to intercooler pipe with Blow off Valves circled

EDIT: Found some rubber caps to use instead of rubber chair leg bottoms
http://www.mcmaster.com/#92805K28Updated pictures with the new caps on from mcmaster - didn't know they were going to be red