Tell him not to do it. If he is buying new, it will be more (generally) than an investment value (if it isn't, the company has underpriced it, which, trust me, never happens), so he will have to wait for a substantial increase in value just to break even and with a Hublot that may never happen. If he wants something as an investment he should buy an old classic mechanical watch at an auction and keep it for a while. At least then he will know he is getting something at its investment value and, after that, more time, should be more money.
Just out of interest, is he planning to wear the watch, or just keep it somewhere safe in its box?