Saddle soap or leather grease?

So basically I'm doing a show in May. It's on a riding school horse (I don't have my own) so my aim is to look dashing for the day - doesn't have to be long lasting since I don't always get to ride that horse, other people ride her too, and anyway she's not mine, however much I would like that.

I was looking at buying this: Decathlon - MAINTENANCE-REPAIR MAT-TOOLS leather - fabric care grease FOUGANZA - Leather Grease 150ml FOUGANZA - NOURISHING leather.. First things first: this may sound silly, but will it make the saddle slippy (I don't want to fall off!)? I'll probably be cleaning the tack on the day, since I'm just coming back from holiday the day before. Talk about bad timing.

Will saddle soap be a good alternative? I'm not awfully keen on it, since it's more expensive and the one time I have used it, the tack looked pretty much exactly what it looked like before I cleaned it, and I want the tack to have a shine to it.

First, is it your saddle?
Because if it is yours then you might as well go for grease. You can even do soap first to get the dirt out, and then use the grease to nourish the leather and make it shine.
You can use grease by itself, but I prefer to clean the saddle first just so the nasty things don't stay on my saddle, but that's just me.

Then, I see your are buying from decathlon, well known store in france, where are you located? If you have access to decathlon, I would suggest a grease that I have been using for 10 years now, and it is awesome!
My saddle and half chaps are about 5 years old, and my bridle is almost 10years old, and all in excellent conditions. Thanks to my grease

EFFAX BAUM CUI- GO SPORT

This is another french store, but if you google effax lederbalsam and find online stores that carry it