I've had a pair of these MT91 boots since last winter:
They are incredibly comfortable and warm, I'd go as far as saying that they are the best winter cycling boots I've ever had in about 25 years of cycling.
I can't really fault Shimano footwear and I still have a pair of the M110 shoes in good working order which I bought back in 1993.
All the other brands I've tried have always fallen apart after a year or two.
Yes they are excellent. You need to try them though as i had to go up a size. 42 fits in a shimano, but my 81's are a 43. Very comfortable and very good.
Good winter boots of whatever brand are worth the money. I've had Shimano D100s and currently have W101s ~ been very happy with both. You just can't beat having warm(ish), dry(ish) feet