Although I'm not a synthetic fan, I do admit that Fabtron is about the best I've seen. Reinsman has always made a good "off the shelf" product so I would suspect that their synthetic/leather saddle would be up to their standards.
Although You can't "turn" a stirrup with a broomstick on a synthetic fender, you can do it permanently in a different way. I do all my saddles like this:
(You can skip steps 3 and 6 on a synthetic)
1. Remove the stirrups.
2. Remove the Blevins slider but remember which way it faced.
3. Soak the bottom half of the fender (the part that holds your stirrup)
4. Put the Blevins slider back on but facing the opposite
side of the leather.
5. Put the stirrup back on but twist the fender so that it attaches to the opposite side of the fender (the one with the holes).
6. Put the stirrup hobble back on very tight to hold the twist in place.
7. Let it sit overnight or until dry then oil the leather.
What you end up with is a stirrup that will always be in position to receive your foot as you mount your horse. It gives you the added comfort of eliminating the torque on your knees.
The following are some pics of a new saddle I just finished turning.