The XGK is a simpler design than the Nova. I'm not sure why the XGK won't simmer, but it doesn't. I presume it's the valve design, but I've never bothered to find out. The Nova is more of a general use stove than the XGK for that reason.

I have both, but agree that for the average camper, a canister stove is much easier to use. I have a Primus Micron and a Coleman Xtreme. The Coleman is an orphan. You can still get them online, but one of these days the cartridges will be also be discontinued, so I can't really recommend it. My XGK is over 20 years old and I can still get parts for it from MSR.