When I bought my Yamaha P45 plastic piano, I bought a few accessories for taking it out on gigs (this bag, and a folding keyboard stand and a folding seat, sustain pedal & eventually added an expression pedal).
Despite being advertised in places as for slimline 88 note keyboards, it fits my piano without any trouble—which I would not call slim, especially with my added folding music rest still attached (together they're 1.35 m wide, 33 cm deep, and 21 cm tall). Plus the pockets can hold the pedals, cables, power supplies, and music.
My piano weighs 11 kg, to start off with, so it becomes a bit hefty to heave around. Using it as a single-person-carry with its shoulder strap is a bit much, I think for a bag of its size (and its potential workload), a couple of handles at each end for a two-person-carry would have been a very good idea. While you don't need handles to carry it that way, it would help. Especially when you need a spare hand to open a door.
There's two handles in the middle, with a velcro wrap-around joiner to keep them together and give you something a bit wider to hang on to. Unfortunately the stitching is coming off the velcro, that happened after taking it on less than a dozen gigs.
It's padded and protects the piano fairly well for people who actually take care while transporting their equipment. The pockets are not padded, and care needs to be taken when things are in them (from them being damaged, or power supplies getting squished so their prongs poke through the bag into the piano). And any keyboard with protruding knobs will still be in danger of having its knobs broken.
There's a rubberised strip along its spine which should help when people skid the bag in and out of vehicles.
Inside there's some velcro straps that can be used help hold slimmer keyboards, or any keyboard, in place while you're manipulating the bag into position to zip it up. The velcro's a bit sharp, and you have to be careful not to let the edge of it rip into your fingers while wrestling with a heavy keyboard.
I thought the price was a bit much when I bought it a few years ago ($119AU minus a discount), and I see it being sold cheaper now. It's really only the velcro and handles that I could complain about.