A websearch on "Buckfast Bees" will give you many websites with largely the same information, including the usual information about Brother Adam and the history of the Buckfast bee. They virtually all mention "Isle of Wight Disease" and state it was caused by acarine. This is the old view that has been thought to be incorrect for many years, yet none I looked at acknowledged that.
Many beekeepers seem to think that Buckfast are a breed of bee, but they aren't. It is popularly seen as a hybrid, but then some sources suggest it is a "hybrid between many races". This in my book makes it a mongrel. Br Adam himself, in an article in "Bee World" in 1950 states "The Buckfast bee is a cross between the native British and the Italian bee".
Buckfast bees are very prolific and can build up into huge colonies. Br Adam designed the "Buckfast Abbey hive" that used 12 Dadant frames, instead of the normal 11 that are use in the Modified Dadant, that has the largest box commercially available.
I have never used Buckfast myself, but I have handled what I have been told were them on many occasions. If correct, then they were very variable, both in colour and characteristics. Some queens are very light and some very dark, with drones and workers being very mixed colours. This observation has been supported by some of the supplier sources. If Buckfast are a cross between two sub-species then they are a hybrid and the resulting hybrid vigour is probably the reason for their reputation as good honey producers, but surely that is for only one generation. If the queens are replaced by the bees, then we have nothing different than the vast majority of other bees.
My first experience of Buckfast was in my early beekeeping years, when one of my BKA members had 4 colonies in his garden, close to a church. He was a "let alone" beekeeper and his method was to requeen all his colonies in April every year with Buckfast queens, put supers on and leave alone until August when he took them off. When everyone else was averaging around 30lb of honey he was getting 100lb. The queens were raised abroad, I think in Isreal at that time. Attempts were made to leave the queens for a second year, but they often swarmed and when the daughter queens started laying, the colonies often turned very aggressive. This has often been my experience ever since. In those days Br Adam controlled the breeding and sale of Buckfast queens and I never heard a bad report all the time the original queen was in the colony. With a number of breeders in several countries it is difficult to understand how there will be consistency.
Since Br Adam's death, the rearing of "Buckfast" queens has been continued by beekeepers worldwide and there are those who do it using the principles set out by Br Adam. It looks to me that genuine Buckfast, or those bred along the proper lines, are usually quite good, but there are some that aren't. I know there are "breeders" who buy one queen, then raise a lot of queens from them, have them open mated in their area and call them "Buckfast". I have seen "Buckfast crosses" advertised, but what are they? Surely no more than mongrels that are likely to be very variable. These are referred to as "fastbuck" and probably are a cause for concern amongst genuine breeders.
I was once invited to an apiary to "see my new Buckfasts". There were four of them and they were as variable if not more so than any of those I have seen from beekeepers who take in swarms. The colour of queens, drones and workers varied considerably and so did their temper! I don't know where they came from, but I would have culled them all - and quickly.
Despite what is sometimes said about breeding from Buckfast, I believe that to avoid some of the problems I have seen you should replace queens regularly from a reliable breeder. This of course adds to the cost of beekeeping and takes away one of the major joys - queen rearing.
A rather amusing story I have is I gave a lecture on "Bee Improvement" to quite a large audience. At question time an attendee said they had "native" bees. I was a bit suspicious so I asked where they came from. I was told "they are Buckfast and they come from Devon, don't they?"