Hi, i have a nimbus oracle 24" and a nimbus 26" Muni. in my opinion as you have a 29" i would go with the 24" as it will be more different where as the 26" is more similar and you might find that you still want to get a 24" afterwards if that makes any sense. 
as an owner of an oracle i can say i have never experienced problems with the aluminium frame or the brake but it is still quite new so might be problems later on. the thing i find most annoying with the oracle is the rim width of 42mm as sometimes when side hoping up hill the tyre bends under the wheel whereas the KH has a 47mm wide rim so i guess this would happen less/never happen but i don’t know as i have never ridden one.
overall i would say the oracle is a very good Muni and i am a big fan of having a brake for Muni.
I would recommend the oracle but i would wait and see if some one who has a KH posts to see what they think so you can hear both sides
When considering which to buy i started this thread it might help
(i wrote this just after waking up so sorry if it makes no sense)
I hope this helps