No big expert, they should chime in soon, but I do choose leather for many things. Before using any product I would be checking what leather, which tanning process and any caveats for that leather. Many but not all leather products use a lacquer finish so conditioners are not really useful if the lacquer is in good condition.
On watch straps, I have found that some German made watch straps on quite expensive watch brands have had a life of about 6-12 months and then they have disintergrated, while artisan straps using sweat resistant leather lining and various outer leathers have lasted many years. The more complex the strap and unique the leather, the more difficult to say. Common un-lacquered bovine leather is pretty receptive to conditioners but colour change is always a possibility.