Like anything there are pro's and con's that need to be considered.
For the Magnum Boost
Pros would be:
Lower cost compared to PCV
compact size
Ability to add fuel
Cons would be:
Unable to remove fuel
Difficulty splicing in wiring (easy to get it wrong) or the need to create adapter as mentioned by Rangemaster.
It's not plug and play. You either need to AFR gauge on the bike to get the adjustable setting right to achieve a desired AFR (no guaranteed result)or just guess.
Also, adding a constant additional amount of fuel right across the rev range won't fix all problems.
I downloaded the PCV software and opened up the map made for Vulcan S 650 with a TB exhaust. There are areas around the 3k-4k rpm range where they're taking out as much as 20% fuel. Once it gets up to 4k-5k rpm range they're adding around 20% fuel but in the 5k-6k rev range there is little to no fuel adjustment from the stock tune. I have a screen shot of this highlighting the clouds of major change where you can see the most amount of map adjustment. I'll up load it when I get home.
For the PCV
Pros would be:
Actual plug and play. No splicing. Harness is pre-made for our bike with clear and detailed instructions including photos on a real Vulcan S.
Dyno testing or AFR measuring not essential. Unit comes with tune to suit stock bike. They have made small adjustments to improve the from factory bike already.
Additional map available for free to suit TB exhaust which would be very similar to most aftermarket straight through exhausts. This can be flashed to unit via the PCV software.
If you want to adjust your map further because of other mods you have done you can also use the optional extra Auto tune module which will store and use fuel trims to keep closer to a desired AFR by itself. This will not endanger your bike as you can set limits (eg. +/- 5%) as to how far it will add/trim fuel from the current map to reach the desired AFR.
Ability to control ignition which is a huge advantage. It's not all about +/- fuel.
Cons would be:
Requires a degree of mechanical ability. Injectors, ECU, and O2 sensor all need to be unplugged and/or adapter fitted to connect to PCV module.
Requires a small amount of computer knowledge if you just use the provided maps without modifying anything yourself.
Higher cost compared to Magnum Boost
Requires a PC if you want to flash a new map or utilise the Autotune features.
Slightly larger than Magnum boost but still very compact.