Is it unsafe to buy into global ETF?

Everything is a risk, but holding USD currencies / USD -denominated assets as compared to other developed countries currencies etc euro/pound or emerging market etc rmb/ringgit/rupiah is the least of worries

Currency Exchange risk (with every deposit and withdrawal) is definitely significant, especially if you will be transferring funds regularly as part of your regular investments. If Stashaway allows, you can make use of external apps like TransferWise and Revolut to fund your account. These platforms allow you to convert SGD into USD at the best rates out there, then you can fund your Stashaway acct from these platforms.

I answered a similar question in detail here: https://seedly.sg/questions/what-s-the-cheapest-way-to-fund-a-saxo-account-in-usd

If you're keen, here's a referral link for TransferWise (for fee free transfer of $900):

https://transferwise.com/invite/u/sebastiank815

Hope this helps! :)

https://transferwise.com/invite/u/sebastiank815

StashAway will convert the SGD amount into USD to buy into the ETFs. Depending on the exchange rate, sometimes it is higher or lower, the amount of investment will vary. Likewise when you sell your investments, the exchange rate will come into play.

If you want to partake in the potential growth of the overseas markets that the ETFs invest in, then you have no choice but to take the currency risk. Consider it as one of the costs of investing.

One alternative to avoid currency risk is to invest in their income portfolio which is SGD denominated. But there is the concentration risk of exposure to a single country market.

Have to weigh the risks for yourself.