Hi,
I responded to a similar chain of posts on vfrworld
https://vfrworld.com/threads/booster-plug.52800/#post-644333
"...in case it helps anyone, here goes;
I can't speak to how effective they are on a VFR but I have owned two other bikes and fitted a Booster plug to both. One was a 2003 Triumph Sprint ST 955i and the other, a 2012 BMW R1200R Classic. The plug made a difference at low revs around town. Smoothed things out a bit and prevented cutouts on the Triumph and to some extent on the BMW. The latter runs v lean so stalls still occasionally happen. Still have that bike. Yes, they are over-priced for what you get but they are not snake oil and do make a difference. You can read more about what they are actually doing here:
https://www.boosterplug.com/shop/cms-how-it-works-full-version.html
Were there noticeable gains in speed/acceleration?...not really, but the fuel to air ratio seems to have been helped as the pull on both bikes was smoother and just seemed to have been assisted by the plug. There were no negative ramifications to speak of. Did the plugs change the bike dramatically, No.
A PC 5 or Rapid Bike will likely set you back a LOT more and given what the VFR engine is capable of and the bikes overall power to weight ratio,...the booster plug might be a better investment. I have no experience with either of these two technologies so maybe they are great. Can't say - defer to those who can and have never brought any of these bikes to a track and I believe both the PC and RB tech is s'posed to shine there more than around town.
I'm in no way affiliated with the manufacturer of the booster plug, just trying to set the record straight as somebody who has experience using one on two bikes. May even try one out on my 8th gen. VFR, but as somebody already remarked (here or in a sibling post), Honda build such a stonking good engine...I don't have much of a need on the 2015 VFR, because it has so far never cut out and just Hondas-along. It is a heavy bike so I'd be surprised if anything made a huge difference to that bikes overall performance low down or higher up the rev range."