How does that work Colin? It could be something useful for us at work, as we get a lot of older BB's to repair.
The nut is loosened off and that allows the part that is split into 6 sections to reduce in diameter to just less than that of the inner race of the bearing. (You would need a tool chosen to fit the size of the inner race. That company does them in 9 different sizes.)
Insert the tool into the race then grip the body of the tool with one spanner and tighten the nut with a second spanner. That forces the 6 sections apart so the race is gripped tightly.
If there is access from the other side, the tool can be tapped out and take the bearing with it. That is obviously the case with a bottom bracket bearing because the axle has to fit through.
If there were no rear access with a bearing in a different scenario, a slide hammer would be attached to the threaded rod and that used to pull the tool and bearing out.
I am not going to buy a press tool to insert the new bearing. I think I can tap the new one in as long as I am careful to keep it aligned properly. I saw a good hint - tap the new bearing in with the old bearing to prevent damage to the new one.
Alternatively - I may make my own bearing press from a long bolt, a couple of large washers, and a nut. Again, being careful to keep the bearing straight as it is being slowly wound into position .