I use Lovinmybags For Handles Only cream on almost all my bags with vachetta (except Galliera for fear that it may smear the brass rings) and I LOVE it! It protects the vachetata against oil and dirt beautifully - this is especially evident on brand new bags. The vachetta on my Tivoli PM and WC pap for instance is still a light, even, clean patina after almost a year (I use them roughly once a week). Just be extra careful not to apply too much at one go, especially to area near the yellow stitching and any hardware.
For pre-loved LVs, I always clean the vachetta with baby wipes first and allow it to dry completely before apply any FHO cream. This is important or else any existing dirt may be "locked in" if the cream is applied straightaway. And of course, it may not do much to bags with dark or very dark patina.