My first experiences with Medical Texts while playing the 1 core set Roland Banks starterdeck were terrible. After I was done, I buried it at the bottom of the game box and vowed never to use it again. At the moment the healing options in the game are very limited though, so I thought it might be worth taking a better look at Medical Texts.
Medical Texts is currently the only card that offers "unlimited" healing, which is a good thing. The problem is that it's a card that doesn't get along with just any investigator, as I found out the hard way.
Put it in the hands of Roland Banks and it's a not so reliabe heal that you can waste a precious action on while getting damaged in the process... Time after time... after time... But if you put it in the hands of a high intellect investigator like Daisy Walker, Daisy becomes a walking one-woman ER unit. With an un-boosted Intellect of 5, Daisy starts all of Medical Texts skill tests with +3, netting you a very good chanche to succeed. And with Medical Texts being a Tome, Daisy's unique skill will let you use it once each round without costing an action. (True story: I once "Burst-healed" 4 health in one turn that way.)
So in short: with Medical Texts it's all about the investigator using it.
With the deck building rules for the Core Set investigators, the only investigator who can use it reliably is Daisy Walker. But with the deckbuilding rules for the investigators in the upcoming "Dunwich Legacy" permitting using up to 5 cards from your "non-primary class sphere" , Medical Texts could become a good healing option for every investigator with a good Intellect skill.