I make flags which I sell on my Instagram @garagepatriot. Make sure the stain is dry before applying this. Apply the first coat lightly and let it dry 4 hours. If the surface is still tacky it is not dry. Then lightly sand the finish off. Reapply and repeat the steps four times for best results. It may take time but the end result will be amazing. Please see one of my flags (stained wood) which I attached below. This is after 4 coats and sanding in between coats. You can literally see my image in the mirrored finish.
Easy to use no mess covers all areas and hard to reach areas too
No, I've found no yellowing. Of course, treated wood takes on an amber sheen different from the dull flat look of untreated wood.