If it’s cost neutral, i’d choose silicone over monocouche. It’s more durable, more crack resistant and stays looking cleaner for longer due to it’s hydrophobic nature. It’s usually more expensive than monocouche. I’d say you’re comparing an expensive monocouche system with a cheap silicone system there. Ask how much the Weber Silicone is perhaps?
Smooth render systems, of both flavours, don’t patch well if repairs are required and can also be prone to algal growth over time, especially light colours.
Be aware that your smooth white gable might end up green in a few years.