Is MooMoo a legit company?

Custodian brokers are perfectly safe brokers to use. In fact, it is actually not possible to have foreign shares in your CDP account, so a custodian account is the only way to do so.

Custodian brokers hold the shares that you own separately from their own assets, so rest assured, your assets are likely in safe hands. To be doubly sure on their safety, do ensure that they are MAS regulated and you can also look into their history to get a better sense of their stability.

For me, I use interactive brokers, which is the largest broker in the US by daily trading volume and a history of over 40 years in the business. MooMoo is owned by parent company Futu, which trades on the Nasdaq exchange in the US. It is also MAS approved, so in that sense there's a first layer of check that has been done for you already.