I ride the Rivet Independence on my Gilles Berthoud touring bike and I have the Rivet All Road on my Surly ECR. They do not soften like a Brooks or a Gilles Berthoud. Note the underneath has the fabric (for lack of a better word) that restricts the sag and splay factor the Brooks tend to do. Also the leather "tie" underneath will keep it stiffer. My independence with the slot is softer than my all road as it does have some give around the slot. I hope you like them. Hopefully the fitter knows that mounting a leather saddle isn't that same as other saddles. You'll want the nose at least level or slightly tilted up. For sure NO NOSE DOWN. These saddles are slippery, another comfort factor so the last thing you want is to be sliding forward. Having a nose tilt keeps your sits where you want them. Given the hardness I am certainly aware of my sit bones after a long day of riding but the next day I can get right back to riding without pain.
Can't wait to hear the results!

oh on conditioning - I have never conditioned either of them. One is 3 years old the other is almost 2. If we are out overnight, I do cover them and if it is raining I cover them as well.