Hi, welcome to GoY, the red robin has a height and spread of about 15ft, the arbutus, has a height and spread of about 25ft, so neither of them are really suitable to be grown in a container, although you may be able to grow them for a short while in containers, you will eventually have to plant them in the ground, if you want them to reach their full potential, Derek.

Of the two, the Photinia is the best choice for a tub, though what Derekm says is accurate. The only thing with Photinia is, it does respond quite well to cutting, so you could prune it back a couple of times a year to keep it a bit more lively and smaller.

Maybe an Arbutus unedo 'Compacta', or Elfin King'?