How safe is my investment with Tiger brokers?

Your broker should not be able to touch your assets as they should be held separately from the broker's assets. Hence, even in winding up, the broker would not be able to use your assets to clear off their debts and the creditors also do not have any rights to your assets. The only case this would not be so is in the event of blatant fraud (e.g. MF Global). Even so, the clients of MF Global eventually received their funds back (albeit after many years).

As for myself, I do stick to more established brokers for long term holdings and investing. I use IBKR personally.