The replacement injector is the new Cisco Meraki 802.3at model (MA-INJ-4-US). The tech specs are fairly similar with the key difference that the maximum output power of the unit is 30 watts now rather than 19.6 watts. The new device is functionally equivalent to the old.
However, probably most important to note is the price jump. The list price of $149 is $50 more than the old injector. Something to keep in mind if you are upgrading a large network or on a budget.