I do not see any problem to slow down gradually with the engine, even more aggresive slow down would be fine the final drive and the engine has been designed for that, there is no difference on the engine/gear forces you apply when accelerate or brake with the engine does it?
The drive train is designed to propel the bike forward by turning the rear wheel, not having the rear wheel turn the engine with the forces working in the opposite direction.
IPSGAG? Seriously Grahamm no offence, but you do not expect us to remember all this when riding do you
Why not? There are a lot of bikers who know The System and you're probably actually doing it without even knowing it.
When you're riding you are (or should be!) constantly observing ahead, to the sides, in your mirrors etc for other traffic, hazards and so on, yes? That's Information.
When you're approaching a hazard such as a bend or junction or other vehicles, you might think "where should I be that's safest?" That's Position.
You probably slow down for the hazard, ie Speed.
You may change down a gear (or two or three) to get better power response if you need to manoeuvre. That's Gears.
Then, once you've navigated the hazard, you increase your speed back to whatever is appropriate for the conditions. Acceleration.
All that IPSGA does is formalise what you're most likely doing anyway.
And in my opinion is much more fun to slow down after you change gear down how else you can do the sweet screaming banshee sound of the Fazer?? Advanced riding is boring - here I've said it
Your bike, your life, your choice.