Limit orders are a risk management technique. Your limit order will not fill if you can’t get the price you want. A market order is subject to microstructure fluctuations such as flash crashes.
All things being equal if you don’t care much about execution costs limit orders that cross the market are what you want.
I feel like the brokerage I was using would make the purchase at market close (Vanguard index funds). I assume at the market closing price? That gets rid of a flash crash danger anyway.
