neil, i personally don't have experience but do know several beeks here that went with them, not just once but year after year.
one of those beeks, her father kept bees and she has been keeping bees for 35 years. she tried the mn hygenics for about 4 or 5 years i think.
not my experience, just what chatter we had........these beeks typically lost the majority of their hives before winter or early winter months.
yes, treated for mites, yes, left plenty of stores and fed to get through our winter months. minnesota and wisconsin.
this is doc spivaks developed line, they are italians, and the claim is to "have a high degree of hygienic behavior known to be effective against diseases of the brood such as American foulbrood and chalkbrood. This trait is thought to be two behaviors acting in Minnesota hygienic italian queen synergy, the uncapping of diseased cells, then the removal of the pathogen along with the pupae,effectively disrupting the disease life cycle. Another trait, Varroa Sensitive Hygiene (VSH) is especially effective at targeting varroa mites."
first off, Italians do not winter well here in minnesota. italian queens lay very late in the season. and italian queens do not curb laying if there is a dearth of nectar or pollen, she just keeps laying. italians will blow through stores in fall when nothing is coming in, there is no conservation. mite loads will be high.
my beek friends that kept them made comments relative to the mites in their colonies and thought or experienced losses higher than if they had kept carnis. some additional comments about the 'hygenic line' as reported to me were disappointing. just repeating what was passed on to me.
as lee said, the beek friends reported the bees to propolize the heck out of everything (not a bad thing, just a pita) and honey harvests varied. this could also be the environment the bees were kept in here. i guess what i learned from all these beeks was the disappointment in varroa resistance and winter hardiness.
don't want to discourage you neil, just giving you some input from several beeks here i know that won't purchase these bees/queens.