I'm guessing the "Firebird" is actually identical to the V4 standalone? Without the DB9 ports and with the 68k socket soldered. Rebranded and announced as a new product.
This was first announced in August 2017 (
https://www.apollo-accelerators.com/...ement_v1_5.pdf), with the release date set for Q4 2017, and the A500/A2000 model was supposed to be the first to be delivered. The A500/A2000 model of the accelerator never came, and the standalone was released about two years later.