I have a few of the CD based manuals and I can say that if it's TOO cheap, it's almost GUARANTEED that it's gonna be just PICTURES of the pages of a paper manual - not TOTALLY useless, but definitely not as useful as it COULD be - here's why -
The "pictures of pages" means that there is no SEARCH function possible - in other words, say you're working on a differential problem - with the cheapo manual, all you can do is find the PICTURE of the contents page - it might say enough to get you to where SOME of the info is, so you find THAT page - but maybe there's not enough info there, and unless you wanna spend the time reading EVERY picture of each page, that's all you're gonna find -
I've been dealing with tech stuff since I got my first car 61 years ago, and it's been my experience that VERY FEW manuals will tell you in their INDEX pages, where ALL instances of a word are located, just some of 'em -
BUT - if an "electronic" manual is done CORRECTLY, it will be SEARCHABLE - this CANNOT be done from just PICTURES, those pictures of pages need to be converted into ASCII text so the computer can find "differential" as a WORD, not just a picture.
This takes time and effort, so the "cheapies" don't bother - typically a SEARCHABLE version will cost 2 to 4 TIMES as much, but in my experience it's WORTH IT - my "searchable" e-manuals will let me find EVERY SINGLE instance of a word, no matter WHERE in the manual it is.
That's something even a $300 original PAPER manual might not do - it all depends on the original WRITER of the manual, and whether they understood the VALUE of a COMPLETE index.
The GOOD news - it's EASY to make SURE you get the SEARCHABLE version of a manual on disk - if the one you're looking at BRAGS about it being "SEARCHABLE", then that version was created using the EXTRA STEPS to make it "computer friendly", AKA "SEARCHABLE" - If the ad does NOT mention the word SEARCHABLE, then it's almost GUARANTEED that it's NOT.
Think about it - everything you ever bought, if something was a strong SELLING POINT the seller would BRAG about it; if NOT, they just don't MENTION it and hope you fall for it.
Anyway, in my experience with "e-manuals" if they want less than about $40 it's probably NOT searchable - around $50 and up, it probably IS searchable, but if you don't actually SEE the claim, it almost always WON'T be.
There's all kinds of people; every job I've had since high school has been detail oriented, some to the point that ignoring a detail might mean not SURVIVING - so even in retirement, I follow what works for ME - others, maybe not so much, or don't care, or can't afford to pay more for something if it's not completely necessary -
Either way, hopefully this info will help you pick what works for YOU without having to pay TWICE... Steve