I was told by the shop that installed my Ventureshield, that the time it takes for the film to yellow depends on how well you maintain it. Just as @
Pacific_Auto_Films said, Ventureshield also heals, to a certain degree, and they will all yellow, but you can drastically slow down the yellowing by washing it often and apply wax on it to protect it. I never used Xpel so i can't speak to that, but I have Ventureshield installed for almost 4 months now and it didn't change in color a single bit.