I see this is more opinion that anything else and as usual on the internet giving an opinion does little. Still I am going to type my ass off.
I own a decent sized shop that has specialized in turbocharged DSM's (Talons, Eclipses, Lasers, Galant VR-4's and the EVO8) for about 15 years now.
I have tried and sold just about every blow off valve/compressor bypass valve there is.
The first generation DSM's come with a really good valve, as a matter of fact there aren't too many aftermarket valves that perform the duty they are suppose to any better.
The valve as you know is suppose to open when you lift off the throttle to allow the boost pressure in the intercooler pipe to be released (either into the atmosphere or re-circulated back into the MAS pipe) and not stall the turbo. The woo woo woo sound you hear when you get off the gas is the air bouncing back and forth from the compressor wheel to the closed throttle plate, this causes the compressor wheel to try and stop.
We tried a few valves on my fathers WE4 quite a few years ago. It worked well and did what it was supppose to. No gain in HP, ET or trap speed as it is not going to do any for performance on an automatic car. It did cause driveability problems. We had it vented to atmosphere, what happens is the MAS measures the air that is coming through it. When you lift off the gas the air that was measured is not dumped into the atmosphere throwing the air fuel mixture off. Same thing happens if you have a valve that leaks slightly at idle, as does the DSM valve.
Here's more useless information. The way to fix this is if you are going to run a MAS on your Buick and a BOV then simply put a nipple on your MAS pipe and route the air back into the system after the BOV releases it.
On a speed density car the lost air from venting it to atmosphere has no effect at all.
More information
Most aftermarket valves have an adjustment on the top of them. They also come with different rate springs. The adjustment and spring rates will effect how the valve opens when you snap off the throttle. IF the spring is too heavy or the adjustment too tight it will not open at all or enough. In this case you still get compressor surge. On the same note if you get a spring that is light enough and don't tighten down the adjustment bolt so it does work properly then you end up with either a leak at idle (fine if speed density or routed back in) or you get a leak at high boost pressures.
Ron's car (Rapid Automotive) that I race is Ken Duttweiller's old car. Ken built the car, it made 1485 hp. The car has two expensive turbos on it. The same turbos are on the car now as when Ron got it, NO BOV's. My tube chassis DSM runs 7.8's at 175 mph, NO BOV's. Both these cars are automatics.
After realizing that BOV's either leak or don't work as they should when they aren't leaking I have pretty much deleted them from everything I own. This includes some high HP 5 speed manual trans cars.
I have not personally seen a turbo fail from not having one. Maybe back in the old days when aftermarket turbos weren't what they are today they did.
My advise, especially on a Buick. Save your money and don't buy one. IF you do decide to buy one, call us I'll give you a good deal on anyone you want! haha
Take care,
David Buschur
www.buschurracing.com