OpenSprinkler Latch uses the same firmware as other OpenSprinklers, and yes you can easily turn on/off a zone manually from the homepage. No programs will run unless if you configure some programs and enable them. The same HTTP API works with OpenSprinkler Latch just as the other versions.
The firmware does not support pressure sensor — if you need pressure sensor reading you will need to modify the code to read the sensor and output that through HTTP so it can be displayed on the homepage. The coding isn’t complicated, largely involving following the examples of existing code.