Thoughts on Brôkhyr Thunderkyn?

Hi, fellow kin. I just got given as early three wise kings presents( Spanish Santa Claus) two units of Brôkhyr Thunderkyn. I am not sure how to build them and how to run them.

As transports I already have a chunky fortress and a Sagitaur (but I think I can’t use it as a transport for them).

I thought about magnetizing them but I think it might be hard with their tinny hands. So which option should I build them as? And how should I use them?

Many thanks in advance. Rock and stone