Not a bad little starter unit for the price. The pump is light duty at 5GPM, and small 3/8" hose, fine for lawn spraying and small tree shrub spraying eventually like you say and yes you can flush the tank for safe insect control apps after using weed controls.
Like the idea of future use too for a nurse tank. I have a 300 gallon unit in my truck that I use specifically for a nurse tank and tree sprayer.
Good looking out for not wanting to over load that half ton too. Spray mix is basically 8.4lbs per gallon.