Good Lord,

If stall strips were ineffective on models, then I suppose washout should not be used on model wings either?!?

As most of us know, many designers, especially of scale models, use washout in the tips of their designs to help make the stall more benign.

With respect to stall strips, yes they can be used with good effect on a model.
Before implementing their use, make sure you laterally balance your plane, across the wing tips.

Then the trick is to test fly the plane and try to determine which wing needs the strip. This can be determined by seeing which way the plane falls off in a power off stall as you simulate a landing flare, up at altitude.

If the plane always falls to the left, apply a small stall strip with tape to the right wing.
You are trying to get both wings to stall at the same time and have the plane stall straight ahead.
The only way you can determine size and location is thru trial and error. Unless you can tuft your plane and install a camera to monitor the airflow.

I used this method to help tame a nasty tip stall on a Great Planes 72" CAP 21 back in the mid 90's.
Worked like a charm.