If those truly were 'the good old days' then the brothels would be regulated by the government for quality and safety and be legal. Or possibly run by the Church, as they were in Hindu nations. This is just facetiousness, not true sexual education.
Brothels in Europe were run by the Roman Catholic Church in times past, after the anti-sex rantings of Thomas Aquinas. They made profit out of condemning sex, and then offering sexual gratifiction for money.
In much of Europe until the second world war, brothels were legal or somewhere along that line. Then things changed, although not totally. In the UK it's quite legal for a woman to work as a prostitute, but the sex industry is not legal in other ways (very complicated). In some other European countries, prostitution has been re-legalised, following the lead of Australia. Legalised prostitution encourages quality (there is more supply, so working women have stiff competition), as well as safety.
I have had sex with escorts and prostitutes from time to time, and I have learned some tricks from Asian girls in particular, and Asian prostitues are very, very popular in Australia because of this. But by and large, a man is not going to learn much from most prostitutes because they mostly do what they can get away with. An experienced man can have fantastic sex with most prostitutes, I know this for a fact, but it takes experience to make that happen. As a way of learning before marriage, I think not, although good for relieving sexual tension, and exploring fantasies as well (if you're experienced).