I have a 3-9x40 monarch and the new 2.5-10x42. I really like both. To me the advantages are 4" fixed eye relief and I think it is less forgiving of eye position.
However it costs quite a bit more than the 3-9 which can do that same thing that it can magnification wise. Also I think it has a thinner plex reticle, than the old monarchs. However, what I wish they wouldn't have messed with is the power adjustment "knob". On the older monarchs was an easy to grip "bar" on the adjustment ring. Now it is this little knob of some sorts. Cold weather hunting is going to be a pain, because will be hard to get a grip on it with gloves. I fill a lot of antlerless tags, it is a necessity to zoom in, and check for antlers (or make sure they are not forked" before pulling trigger.
If I had to buy another, I would save some cash and go with older 3-9. But I think I'm going to go with Bushnell this time.