Installing a Blow Off Valve is a good idea. It servers two main purposes. First, it preserves the life of your turbocharger and second it increases performance slightly. The reason for this is as follows. A turbocharger increases engine horsepower by increasing the amount of air being pushed into the cylinders. This works well while you have the accelerator pedal pressed because the throttle plates are open and the air being pushed by the turbo is allowed to enter the engine. When you lift off the accelerator between shifts, the throttle plates close and the turbo is trying to force air into a closed compartment. Since the air has nowhere to go, it forms back pressure on the turbine itself. This has the nasty effects of slowing down the turbine as well as applying undue stress on its bearings. Once you release the clutch and get back on the gas, the turbine has to spool up again before it can provide boost.
The BOV solves this problem by providing an alternate path for the air to exit when the throttle plates are closed. The air can be vented to the atmosphere or re-circulated back into the intake. The disadvantage of venting air to the atmosphere is that it makes a "pfffftt" sound between shifts that sounds not unlike that of an 18-wheel semi. The advantage is that you can install it within 30 minutes with absolutely no drilling into any engine parts.
On a Difficulty Scale of 1 to 10, this procedure rates a 3.