Visited the saddle shop last weekend with mold in tow, getting a few funny looks about it. I tested the mold by flipping saddles I liked (and were at least CLOSE to my seat size) over, lining up the front concho to the line of the scapula, and laying it there. I could easily see through the gullet for clearance, check out the bar angles, and contact at the back of the tree! It made shopping much less anxiety inducing for me.
I was confident in a circle y salt river wide I spotted and once I brought it home, fit my boy great! Felt stable through our ride, no slipping during mounting (even with a pretty loose cinch, to test its fit), and made great contact over his back, before and after the ride!
I'd have to say the extra time it took to mold and buy the plastic etc was well worth it for me.