Simon Reeves

I had to reply to say thank you as I was struggling with this, and for the same reason too (deadline submitter!) I noticed the attribute was green but didn't quite twig adding the argument to Get(), cheers!

I tried your scene this time, it actually works fine for me - toggling ‘enable merge 1’ while displaying OUT - the geo updates

this is in 18.0.566 if it helps

Also you say its a python expression, but you are using hscript!

I haven't opened your hipfile so forgive me if this doesn't help - but for conditional switching perhaps you should consider the switch-if SOP, it is very useful - for instance, you could test if a certain SOP has a point count > 0 and switch between different object merge SOPs