Ikea Eket shelves with a large vinyl collection?

Adding a solid back greatly increases the weight holding capability of any shelving/ Also avoids the sideways tilt and destroy of some shelving. The weight can be thousands of pounds!!!
Adding additional VERTICAL bracing... particularly in the bottom units also adds to strength and stability.I use Sauder TV stand box and cube (all have a solid back) up to six high. with the added bottom verticals... Have used for 15 years, 6,000 LPs, (now down to 4,000 as I get older... Never a problem.

Quite right, Elizabeth. When I checked out the EKET and the Kallax at my IKEA, I saw the EKET had a back panel, the Kallax not. I pushed on the side of a 16-cube (4 X 4) Kallax, and it moved---a lot. When I assembled my EKET's, they "gave" a little when pushed (not nearly as much as the kallax), but were very structurally stiff after the back panel was slid into place. It locked the whole structure together.

Fwiw, I decided on the Kalax, 2 units of 4 cubes, stacked and connected via barrel bolts. I could not be happier with them and plan on adding a backing panel for additional stiffness.  But that has time and is not a priority. I did add some felt pads to the bottom unit to facilitate ease of moving as required from time to time.

I have to admit I never even gave Ikea a thought for record storage.
I got my shelves from Amazon, will have to see who they were made by, but each unit consists of a 4 compartment cube at approx $60. No back but the outer wood is an inch and half thick so it ain't moving! The no back annoyed me for albums going too far back so I just added some flat wood " bars" to the backs( 2 on each shelf) which stopped them all in same depth. I feel the house will fall down before these will.

Last week I saw my ikea was having a sale .My kind Chinese neighbor took me down in his truck and I bought a 16 cube Kallet for the grand price of 78$ + tax.
My kind Chinese neighbor and his son are very handy and put it together in a half-hour and wouldn’t take a dime .
Satin black looks elegant on my wall space and REALLY helps in my small condo !