As mentioned above, wind is a big factor. The Montana is very flimsy and also has a sheen in certain light conditions. The Dutton is much more stable yet bulky, and with just one post, can spin in the wind.
I like the Heads Up idea, but again, with any wind it could greatly affect the shot, same with the umbrella.
There's a hole in the back end of the Dutton, we stick an extra arrow/metal rod in there for a second point of stabilization. I know that sounds bad...it is what it is...it works :)
Mt.man et al, I made a mistake...was thinking of the Renzo which is in fact flimsy and has the sheen. I haven't used a Montana Pronghorn, but I do have their WT buck...and I'm sorry, but it is also flimsy.
Montana: Very portable and packable, but tough to use in wind like where I hunt.
Dutton: Not nearly as portable, more stable, rotates with the wind unless you double-secure it like SitO mentions. For stationary blind hunting this is a better choice than the Montana if the wind blows. For spot-stalk, not so much.
Elk Mountain Slip: Manageable in wind, easier to walk/stalk behind than either of the above, doubles as a shooting/filming blind, quick up and down. When I draw another buck tag, I'm going with this one for spot-stalk.