I do it usually in 4th 5th & 6th always going up. And not even at full throttle just back off the throttle and shift. I will say that the FZ-09 transmission is not as smooth as most sportbikes! It's not a big deal you can shift in a car without using the clutch.
Clutch! Yes or no?
Depends of what I want to do.
When I'm cruising, I use the clutch. Whem I'm in a ADHD mode I change gear without using the clutch.
When done right it works seamless. Just practice. When executed right you keep the front uder control without uncontroled movements.
Every movement in the bars will give a restless bike.
A long, long time ago, I had a bike with many false neutrals when upshifting. I discovered it never happened if I shifted without the clutch and got used to shifting that way. I've been doing it ever since, no matter how much or little throttle I'm using.
Nearly all motorcycle transmissions have dog type syncro's.
This means the faster you engage the dogs, the less wear you have.
Clutching just takes the loads off the gears to some degree, but does not lessen wear, and the "slower" you engage the dogs, the more you wear them. (Unlike synchro type arrangements, where the taper/cones engage to smooth out the gear change, and wear is higher if you don't clutch every time.)
As long as the gears reach the same speed, they will engage, and with a dog, it's nearly instant when they are firmly engaged. The reason the bike makes a thunk when you engage first after sitting in neutral for a while is part of the gear set is still spinning when you engage first gear and the rapid stop when 1st gear dogs lock in and stop the spinning you get the "THUNK."
The reality is, one gear rack is "attached" to the rear wheel via the chain/sprockets. The other is "attached" to the crank via the clutch. Put it in neutral, and let out the clutch, and you just spin one of the racks at engine speed.
Pull in the clutch, and that rack is still spinning, while the "output" rack is not.
Now click down into 1st, and the spinning rack is stopped by the other rack/sprockets, and chain. (And THUNK!)
Let out the clutch, and it's going to multiply the tourqe at whatever ratio the gear set is designed for and the bike goes forward.
As for what I do? I mostly don't use the clutch after I've started moving, just back off the throttle for a blink in conjunction with shifting to get it nice and smooth.
But I will use the clutch for downshifts nearly always, and at slow speeds to moderate this bike's not so smooth action while tooling around. (Soon to put Kevin's 02 sensor fooler to have closed loop running richer, so it should be smoother, and need less clutch work in theory.)