Mark, in usual outdoor conditions I also use Snee (or now Mtroniks) inserts exclusivley. I hear those Mr O ones are good but I have so many Snee's it's a no brainer for me.
In Mini spikes I think a full Losi or Proline insert is too big so an already firm insert becomes condensed and even harder. In a minipin it's not the same as the tyre shape is more like an american tyre.
What 4wd have you got, are you doing regionals (I missed last weekends
)?