Although the OMF is the default floor these days, its value is overrated; it appeared on the market when varroa first arrived in the UK, and was said to allow the removal of about 5% of varroa though grooming. I have yet to see research to suppport that claim, but it certainly diversified suppliers' sales opportunities.
I have learned that bees will propolise mesh floors to the degree necessary to modulate thermal & humidity levels to maximise colony efficiency, and cooler air near the mesh prevents the drawing of comb to the base of the frame; bear in mind that 35C is needed for comb production.
Board in or out? On a windy rooftop apiary, in all year. At ground level, the book says they should be used to test varroa drop for two weeks a year, and spend the other 50 in the shed. Suggest you leave it in until they have drawn any foundation to the base fully.
As Drex said, watch out for wax moth larvae in the board detritus.