This cage is fine I have one and it's comparable to a brisbane minus 1 door Brisbane measures approximately 63" tall (36 off stand) x 33" wide x 22" deep and is appropriate for 2-3 gliders.
One door isn't that bad to deal with the only thing I find a little awkward is hanging things from the top otherwise it's no different than a brisbane.
I have a huge custom cruiser wheel in mine plus big floor toys.. if you can't fit it in the door you can either unscrew the top and put it in from above or slide the grate out and put it in from the bottom.
If you hang the sleep pouch on the left side wall or right on the door itself it's easy to get in and out despite only having one door
The 2 things to keep in mind is 1 making extra sure the latch is actually latched. Sometimes it looks latched when it's not and they will get out. Just get in the habit of tugging on the door after you latch it to make sure it's actually closed.
2 depending on how little the joeys are.... the spacing between the corner and first bar of each panel is wider than a half inch on the one you posted and the brisbanes. The rest of the bar spacing is a half inch but the corners ARE wider and small joeys CAN and have get out through them, in one unverified case a larger glider got stuck in that spot and passed away.
If the joeys are small and figure out they can escape you can use hardware mesh and zipties to secure the corners of the cage but you want the mesh on the inside so they don't get trapped between the bars and mesh,.