11.5.2.10 another device we are using (same story) is equipped with 12.1.1.4 we want the same version on both devices. So the 12.1.1.4 would be good (or a newer version so we equip both devices with this version).
So buying a extreme networks device always includes the risk that if the distributor will went bankrupt, then the device will be transformed into a purple brick. That was new to me.
