I've got some experience playing from the original published editions of various pieces. If you want a visual feel for the differences go have a look at IMSLP's scans of period notation against modern editions their contributors have prepared (many of which aren't the pinnacle of modern music engraving, but are still way, way easier to read).

There are a number of reasons for why it's preferable to play from a modern edition if you're a modern musician. While we can of course learn to handle the older notation, we're battling with two different factors - firstly, the printing technology (or handwriting, if we're playing from copies of the composer's autograph score). As one might expect, music printing in the 17th century was nowhere near as clear or easy to read as modern editions can be, because of technical limitations coupled with various ideas they just hadn't had yet. And you get some features, like beamed quavers, which show up in handwritten music before the printers could do them. I'm pretty sure most of the originally printed music was intended to be studied and memorised rather than played at full speed from notation as we expect a modern orchestra to do. Musicians employed in ensembles at various courts around Europe would have been expected to do this, but they would've had handwritten music possibly prepared by the composer themselves (who would also be working for the court) for that occasion. And of course they would have been familiar with the musical handwriting conventions of their era.

But really the thing that gets you is that written musical language has evolved over the centuries. So if you go back and try to play from a facsimile of an original edition you're likely to run into all sorts of fun things, such as:

- music from before the invention of bar lines has no bar lines, and it's amazing how hard it is to learn to play without them these days

- accidentals didn't used to mean that it applied for the rest of the bar, as it does today, partly because they were invented before bar lines were invented

- accidental symbols themselves aren't the same as they once were

- the convention for notating key signatures has changed

- the convention for notating time signatures has changed

- because ledger lines are hard to write by hand neatly, and hard to print as well, there was a much greater diversity of clefs to allow parts to fit more comfortably within the five line stave. Modern musicians are used to playing from one or maybe two clefs on their instrument of choice. Some baroque concert programmes probably took their musicians through three or four of them on the same part between pieces or movements. To read these you need to understand what clefs actually indicate and be able to unmoor your brain from the fixed idea of what the bottom line of the stave represents.

- ornamentation marks have changed, and composers made their own up anyway

- performance conventions have changed (although modern editions generally don't go too far in putting those conventions into the notation because they're way too messy to notate even today, some of them do talk about them in the preface material)

- a lot of music from the time is full of mistakes, which can often be identified by comparing multiple sources of the same piece

A modern editor preparing a new edition of an old work will be rewriting the notation to modern conventions, adding bar lines, reworking key signatures, changing the clefs, fixing mistakes, adding explicit markers for what would have been implicitly understood accidentals in some styles, maybe changing ornamentation marking to something more readily understood by a modern musician... it's a big job.

Which is why the copyright in performance of these editions is defended by their publishers, because someone had to pay for all of that. If you want a copyright-free recording you have to go back to the originals yourself, as well as finding willing musicians and engineers to record it.

And after all that work... the layman, and the lay-algorithm, probably won't be able to tell them apart anyway.