I believe the "Convert" option is the same thing as the trade page, it just uses a more "friendly" interface.
If you want to save on fees while trading, make sure that you're holding BNB in your spot wallet and when you withdraw, choose the USDT TRC20 option instead of the ERC or omni token.
It is simplier and more friendly maybe. Convert is for lazy people who don't want to spend time to find good offers and choose trade partners on P2P Binance or don't want do few steps with tradings to convert their crypto from one to another.
Convert has a minus point: spread. Binance frankly presents it in their FAQ:
https://www.binance.com/en/convert (click on View more).
6. Are there any trading fees?
We do not charge any fees on OTC trades. However, there will be a spread (if you are buying, our prices will be above the market price. If you are selling, our price will be below the market price).
The spread effect is same on other exchanges/ marketplaces. Accept wider spread and use Convert. If you don't accept it, do it manually with a bit more time.