They brought it back out a few months ago. The one on their site is the only option they are making. It is available though.PSA Discontinued the 6.8. Not sure why it is still on their website.
Id go with a standard lower, ARP barrel and bolt.
I have a AERO upper and lower set aside for a 5R 12.5" ARP barrel when they come back in stock.
Plenty of info here.
https://68forums.com/forums/index.php