The Vertex 4 is run off Indilinx's Everest 2 controller, and the first product to be wholly directed by OCZ since its purchase of the company. The hardware may be Marvell, but the firmware is all Indilinx.
Given the delay in seeing a third generation SandForce controller, it seems that the move has paid off for OCZ, with the Vertex 4 providing some tasty numbers indeed.
The M in the title denotes that this version (the VTX4-25SAT3-512G.M) uses Micron NAND instead of the usual Intel, which is used by the rest of the range. At AU$439, it's not a bad deal at all. While there's some forum chatter about Micron NAND being slower than Intel, OCZ's spec sheets are identical between the two.