Is TD Ameritrade a great broker for investors in Singapore looking to invest in the US? The obvious reason is zero commissions, but what are other considerations to take note?

Yes TD Ameritrade is a good platform recommended by many. However, the account opening takes nearly 2 months before you can start trading.

Do note that TDA have a withdrawal fee of 25 usd. This is also one of my consideration about using TDA as I feel that even though they are commission free, but I do not want to be restrain by the withdrawal fee as in the even that I needed money for bto/renovation/medical or what, I will want to do partial selling of stocks and withdraw the out the money.

Hence, I am using Tiger Broker instead as their comission fee is significantly low (min 2.00 usd per transaction). And I can do withdrawal with no constraint. Not only is it ideal for trading in US market, but also SG market.

There may be some lag especially during heavy market volume or sell-offs after the opening bell. Experienced this a handful of times recently. But if you are holding stocks for long term, it won't affect you much. Also experienced delayed / lagged pricing once on the desktop application which caused all my option prices to be weird. Resolved this by monitoring the mobile app instead as this is apparently on a different server.

Other than the above mentioned, it's a great platform. Been using it for a number of years now. Great charting tool as well if you are into technicals.