These boots are comfortable... for the first mile.  After the second mile my heels began to hurt.  Not a problem I thought, there is a break in period.  I walked about 5 miles the first day.  The second day I simply was not able to wear the boots.  My blisters were huge.  I waited 2 days until I tried them again.  After the first mile, I was limping.  I took the boots off and looked inside: the heel area has a large stitched seem that runs down the middle/back of the boot.  This stitching is raised and was irritating my blisters.  After only some 6 miles, the material had begun to become worn/rubbed off the inside of one boot and was well on its way in the second.  And before you scream that I purchased the wrong size, I have worn the same size shoe and boot for 30 years.  I know my shoe size!  The boots fit my foot perfectly.
The problem, after a quick look at the inside of my old Dunham's, is the quality of construction.  The Dunham has a leather lining that covers and cups the heel.  There is nothing to restrict or abrade the heel.  The Magnum boot material is thin cloth with a rigid heel piece that turns from hard to soft right at the heel/tendon area.  This creates a friction point that constantly abrades my heel.  The aforementioned raised stitching also provides friction.
I thought, after some contemplation, that perhaps my feet had become wider and so ordered the same boot, from Shoes.com.  These wider boots did feel roomier and I set about breaking them in.  The blisters arrived in miles and I had to switch to my old boots.  I tried to break these boots in over a period of weeks.  They never became easier to walk in.  As for the inner heel area?  It lasted about 12 miles.  A look inside found the same erosion of material.
These Magnum boots are simply cheap, chinese made, crap. I won't be buying this brand of boot again.