There are a number of physical formats you can consider when buying platinum:
Having liquid platinum on-hand and ready in the event of a crisis is the best hedge. Being invested in platinum ETFs is fine depending on your objectives, but if you're truly hedging against unforeseen market collapses, you want physical metal in your possession.
Platinum owned through a commodities exchange, or "on paper" is no substitute for physical bars, coins, or jewelry. Exchanges are heavily leveraged, which means if everyone tried to "cash out" at once, there isn't enough physical metal to go around.
Moreover, precious metals are typically meant as a hedge against the complete collapse of the traditional banking infrastructure. If you wind up needing it, you'll want to have it close at hand!
When investing in any asset, including platinum, it's important to keep the time horizon in mind. Prices fluctuate, and over a longer time horizon there's a better chance of your investment appreciating in value.
The last thing anyone would want is to invest money they'll need in the coming months, only to have the market move against them. Talk to your financial adviser, and carefully plan any future purchases.
If you're not buying an huge amount of platinum, you should aim to maintain direct control over it at your home or other property.
If you're investing heavily, to the point where you need a safe alternative location to store it, be sure to go somewhere like Switzerland with strong property rights. It's key to make sure they can't lend or hedge using your stash.