In my opinion, you get what you pay for. A 6mo warranty on a $2k+ transmission is pathetic, at least with the $2k I paid for the rebuilt transmission at AAMCO for my 88 Bronco 2 I got an 18 month warranty. I've never heard of Kormex, sounds like a seller that gets used stuff and cleans it up to make it look pretty and hopes it'll survive the warranty period before it blows up. I'd spend the money and get one at a shop...the $2k I spent was AAMCO doing all the work, Remove, rebuild, reinstall, test, and warranty. I had an issue with mine right after leaving, brought it back the next day and they easily corrected the issue in the valve body, and its been almost 2 years now and haven't had any other issues.
Had a 93 Ranger with the same tranny that's in my 88 Bronco 2 which was rebuilt by a different transmission shop (who is no longer in business) and it didn't even last 12,000 miles, made it slightly out of warranty by 1 month (it had a 1 year warranty) and it blew up again luckily in the driveway this time...and they charged about $150 less than AAMCO and obviously used the same cheap parts as OEM and never did any updates and heavy duty parts. AAMCO I guess does all updates on their rebuilds and uses heavier duty parts as to not repeat the failures that a certain transmission may be prone to fail at.