I've ridden a Pugsley for the last 2 seasons.
They are fun but you need to really think before buying. There is a reason you see so many for sale in the used market.
I was expecting a ATV type of experience, go anywhere do anything.
They are actually only useful in a narrow range of conditions. They are great fun and unstoppable in 1-2 inches of snow.
Much more than that it's tough going. At around 4 they need a broken trail - they just can't push through. There is a tendency for the broken trail to be very narrow and I can't ride a skinny if my life depended on it.
You can't stand up on a hill as you loose traction immediately - I assume something to do with the low ground force.
Around here a snow fall seems to usually be followed by a thaw - the trail turns to a churned up bumpy icy mess that is unrideable. Tires are ridiculous prices, specially studded tires which would be really useful.
Fat bikes are great in the spring - on soft trails the big tires roll down all the ruts and hoof prints, actually improving the trail. The big soft tires are far better than any suspension at soaking up small sharp stuff like hoof prints on the rail trail and double track.