some trials uni rims have holes between the spokes… like those on the xtp fluo style unis. the Nimbus Trials unis do not, from what I can tell.
What are the advantages?
Some have these holes on the inner wall only and others on the inner and outer walls yet maintaining the same strength as the material is taken away from low areas of stress. They do need to be used with specific heavy duty rim tape to stop the inner tube pushing through.
They also look pretty trick Although for me doing a lot of filthy muddy XC rides the idea of all that crud getting into the rim and cleaning make them a no no for me (not really an issue for trials where lightweight and strength is the goal )