His website
https://orangecow.org/
mentions Mk 4. On YT I found this Mk 5 by what looks like him/his team so I assume this is the latest?
https://www.youtube.com/watch?v=BKTCSLbjhtM
I would assume so though I found this supposedly being a “Mk 6” edit and have no idea if it’s legit or “fanmade”: https://www.youtube.com/watch?v=hkHyh-yrPf4