First choice is between feathering or folding and my preference would be feathering. Make for feathering Darglow Featherstream and if you go folding FlexOfold. I have had both, although the folding was before the Featherstream was available for Saildrives.
In terms of sailing performance, the benefit is mostly at lower speeds in %age terms before hull drag becomes the dominant factor. You can expect overall a typical increase of 0.5-0,75 knots. The important thing is that unlike other speed enhancement things like sails it is constant and needs no effort to achieve. There should be very little difference in performance under motor compared with a fixed blade prop and at least with a feathering prop probably an improvement in reverse.
To purchase suggest you deal direct with the manufacturer unless they refer you to an agent. FlexOfold in Denmark. Featherstream are made in the UK but will of course ship to wherever you are located darglow.co.uk/featherstream/ Take the size recommended by the manufacturer as they will do the calculations based on your boat plus will also already have experience of similar boats. I have bought from Darglow, both Featherstream and FlexoFold (they are UK agents) and always exactly right on size.
These propellers are not cheap. Last year I bought a 17" 3 blade shaft drive Featherstream and it was £1800 including VAT. Suspect for your size it will be equivalent of around £3000.
Hope this helps.