Jim Thompson has done a bunch of calculations with a few focal reducers.
http://karmalimbo.com/aro/reports/
I use the meade 3.3 & 6.3 reducers, and I've got a 0.5x that came with my revolution imager. They are all good. I've got a bintel x0.5 reducer and its terrible.
The meades attach to the back of the SCT, then an SCT-T adaptor, then I use a range of t-spacers to the zwo camera. Allows me to alter the reduction.
A cheap okay one is the antares x0.5. IT just fits onto a 1.25 thread. And the ZWO cameras take both T and 1.25".
There's a lot of good help on CN with stuff like this