What are working Proofide alternatives?
There are other brands of leather saddle wax I would consider, but I would be careful about trying random leather conditioner products. If you make the leather too soft you can permanently wreck the saddle.  

Hammock type saddles work by being stiff, not soft. The stiff saddle doesn’t sag much and therefore supports your weight across a wider area. The break-in period is critical as this where you add micro-tears to the leather to reduce any pressure hot spots (e.g., sit bones). Over time this stretching in high pressure hotspots evens out the pressure over the wide contact area, providing the custom fit these saddles are known for.

This works because:


The leather is stiff and can support weight without sagging much; and
The leather can still stretch in places with high pressure.


This indicates a fine balance between stiffness with some ability to stretch. Now soften the leather too much.  It will sag too much under your weight concentrating pressure in a central hot spot.  You can try and add tension to the saddle to the adjuster (which stretches the saddle), but there is only a limited range of adjustments so you may not be able to add sufficient tension, plus you will have effectively shortened the saddle life (i.e., less future ability to add tension).

Now realize most leather conditioners are designed to make leather soft, saddle waxes are designed to maintain stiffness and leather life by providing some water resistance plus a vey small amount of conditioners to offset the leather drying out.  The optimal blend depends on the leather grade used, which the saddle manufacturers should know.

Given that it is fairly easy to wreck a leather saddle if you make the leather too soft (e.g., riding for long periods if it’s too wet), this isn’t something worth playing with unless you are will to write-off the saddle or shorten the service life.