Will this fit my Dell laptop or desktop?

It is a standard 2.5-inch SATA drive, so it fits any bay or caddy made for a 2.5-inch SATA drive. Check that your machine takes a 2.5-inch drive rather than an M.2 slot.

Is it faster than the hard drive it replaces?

Yes. Any SATA SSD is far quicker than a spinning hard drive for boot and app loading. Against other SATA SSDs it is roughly in the same class, since the SATA interface caps speed.

Does it work in non-Dell computers?

Yes. It is a standard SATA drive, so it works in any system with a 2.5-inch SATA bay or adapter. The Dell branding and part number only matter if you want an exact Dell replacement.

For a basic Windows install, office apps and some files, yes. For large game libraries or video work, it fills up quickly; pair it with a second drive.

What is MLC NAND and does it matter?

MLC stores two bits per cell and generally tolerates more write cycles than TLC. In everyday use the difference is small; capacity and interface speed matter more.