Good job I'm only using a T3 housing machined to take a T34 trim then isn't it ?.
All I can say benefit wise is that you only need to do some simple thinking, when accelerating anything rotational the less it weighs the faster it accelerates, pure simple physics, but danny seems to have overcome physics here!!
Whilst very true there will be less stored energy in the form of a heavier flywheel, the only time you will notice is when pulling away, I've only had 9 cars with lightened flywheels over 27 years so can't comment that much, but have found that maybe you need to just use a few hundred rpm more when pulling away of slip the clutch a bit more, nothing that you'd notice really.
On dannys premis I would go and get one made of depleted uranium as this will be very heavy.
If you have a lighter one acceleration is improved, engine has a easier time, as less strain, gear changes are better, so you have a miniscule downside when pulling away but a benefit everywhere else, once that clutch is fully up when pulling away in first any negative is over, all positives from there on, but seems some people only ever pull away, presumably they then stop so they can pull away again.
You can see why no cars used for racing use lightened flywheels, and why they don't pay hundreds of £'s for super light ones, obviously this is due to them having no advantage.
Now consider the stored mass of energy you can get in a 9KG or so flywheel compared with the weight of the car, anyone using a massive turbo with super lag is going to have issues other than pulling away, but once pulled away the lighter flywheel even on a laggy car will make the engine and car accelerate faster, pure simple physics, lost on some it seems, who like to keep a heavier flywheel that resists speed change more and make the car slower to accelerate.
tabetha