Flaperons are generally helpful in slowing things down a bit especially on a those days without much wind. They don't produce as much drag and lift as dedicated flaps so I'd consider them a half way measure but worth doing on many models.

They do reduce aileron response sometimes to the point that rudder is also needed. My experience with them (currently have them on a Goldberg Cub and a Hanger 9 PT-19) is limited to non symmetrical foils so they may be more beneficial on a symmetrical or a plane that has more generous ailerons.

I'd not hesitate to add them and see what they can offer as very often they don't have any increased weight overhead as separate servos exist for the ailerons.

The only requirement is a radio that will do flaperons and most computer radios provide easy setups for them.

In general, I'd say that what they can do for you is to provide a more uniform glide slope between landings. What is meant is that with a good headwind, a model is given X amount of glide slope but in light air X produces too long a landing so using flaperons allows staying with X slope on light air landings.