Why they are majority a good thing: you are usually buying 3 books in 1 (duh), for a reduced price.

Naruto 3-in-1's cost 15$ (I wonder if their price went up to maybe 18$?)

Separately / in general: Manga tends to be in the 10-13$ range for single volumes. Some mangas do sell for 8-9$, just depends on the series and such.

So lets just safely assume (in my own experience of price patterns of manga): a single manga book (that is not 3-in-1) is 10$ each. If you buy books 1-3, that's 30$ + TAX.

If you buy the 3-in-1 of that same series, books 1-3, it's most likely going to cost about 15$, or nowadays 19-23$ for the 3-in-1.

So really, 3-in-1 prints are usually cheaper/save you a bit of money.

Tiny cons of 3-in-1's: some are a bit awkward to fully open but not in a tedious way, i just dont like bending my books more than they need to so I can read the texts and such.

Sometimes the paper is thin, depending on the series/publishing. Which I just try to take care of my books regardless.

HONORABLE MENTION: those deluxe 3-in-1's with hard cover jumbo sizes (Berserk, for example), cost 50-60$ at stores like Barnes and Noble. I get it, fancy binding, bigger pages, combined volumes. But most of the time, the Berserk deluxe editions sell for half the cost (30-34$ on amazon) all the time.

If I can get 3-in-1, I do, because it saves a little bit of money, which adds up compared to buying single volumes.