Actually, from what I have heard, the new Carter Ducks have rather tight bores, so rollouts are not as big of a concern as you might think.
The difference in quality is likely minimal (probably identical), they both are great machinists. Carter hand makes his guns (not sure about Mongo) and has a history and fanatical following. Mongo is newer on the block, but has proven himself with great products. I think most of the reason in the price difference is due to not wanting to make them (they are apparently a pain in the *** to make) and to keep the exclusivity of the Loo based guns. I have not handled a Redux, but based on my Box Gun (minus a user caused issue
), the Carter Duck will be very high quality.