BCM offered the KeyMod rails, and Magpul came out with M-LOK later. The argument over which was better was more or less settled when NSW Crane conducted the test and M-LOK came out ahead. So BCM is now offering M-LOK as well.
The handguards come in various length. 7($171.95), 10($179.95), 13($189.95), and 15($199.95) inches.