Just played an very long game with as the Bene Tlailax and enjoyed it very much.
V 1.8
My experience with the Axotl Tanks has been "meh". While it can be possible to get clones of some highly promoted units (or homeworld units ^^) more often I would experience the some sort of "degeneration", "devolution" or whatever you may call it
"Degeneration" means many copies would lack one or more promotions of the original unit while maintaining the unitlvl/XP of the original. Since I could not afford to disband the weak copies (needed EVERY unit during wartime, damn deity ^^) often one of the weaker units would get more XP than the original one - or the original one simply died. Now all new units would get cloned from the "defective" unit already missing some promotion by default with a good chance of missing more.
Now repeat that cycle several times and you get brand new tanks with combat 1 and 37XP, needing "only" 13 (->50) XP to get to combat 2.
Another disadvantage appears during lategame when it's alot more difficult to get your new units to use the better promotions (heavy weapons, etc).
On the bright sight there are some uses for the Axotl Tanks:
Simply build it only in some cities. That way getting units like mongoose with +40% interception or tanks with +1 movement isn't a problem.
Or build it in cities which produce mainly bombers, artillery - instead of barracks/airport. Those 2 unittypes rarely get promotions, so once you get one good original you can clone it for the rest of the game.
And lastly sometimes you are lucky enough to get more than enough good copies of your lvl6 units before the degeneration sets in.
On another note:
In my opinion the Tlailaxu are strong right now because of:
1) Guaranteed religion, which also grants 1solaris for every city you own and gets you gpp from turn1 as well as a free priest in your cap and better priests overall. Although you can't adopt another religion, you still can spread the other ones and get all their unique buildings and if you fear the diplomatic penalty - simply don't adopt you state religion.
2) The Plague: -25% strength for every enemy unit is, well, insanely helpful

(Maybe reducing it to -15% would be more balanced).
But the way the plague spreads at first and disappears once both sides make peace is nicely done
My impressions so far from another fun game of a great mod.
P.S.: Please, please fix those no ships. Or add an option to disable them altogether. Even if they get a national limit of 3 and without the army moving glitch they are still extremely annoying (for me) and extremely deadly (for the AI). Annoying because I need half an army to escort my workers, deadly because I camp on the AI's military resources and pillage them as soon as they are rebuilt.