I guess it depends on how much you like it overall.
But given that there aren't too many volumes (and depending on how many you already have), and new ones won't be coming out that often, it doesn't seem like it would be too big a hassle to keep up with, even if you're not liking the newer stuff as much.
I've never read the series, but I was surprised to see Viz did 3-in-1s too.
Yeah, it's more a "do I like this enough to keep it?" But yeah, going to have to do a reread to figure that out at this point.
It's not a huge series or anything, but I've been trying to trim wherever I can justify it. Have roughly 3000 volumes, and that's just too big, especially when I haven't really stopped picking stuff up, and I have a decent collection of western comic stuff, too. Already purged a lot of stuff I didn't really like that I had picked up randomly over the years, but there's still a lot left in a grey area where I'll have to reread to answer the key question of "will I ever want to read this again in the future?" to decide if I'll keep them or not. Just had thought for a while of D Grayman as a series that I liked a lot, but I realized on re-examining it that I don't know if I'd say that or not anymore. (Plus like I said, have like 7 volumes missing on that one, so it has the additional "is this worth investing more money into?" aspect too, which is how I purged a number of series in the past.)
Manga has that problem where it REALLY adds up, because like, if I like a comic run I can buy an omnibus or two generally and be done, but if I like manga, you can end up with stuff like One Piece, Jojo's, Detective Conan, and Hajime no Ippo where they single-handedly manage to take up a significant chunk of my stupid huge collection (plus, even "smaller" series in the 10-20 volume range take a lot more space than a shorter comic run, haha).
Ideally eventually I'll move to what I do with comics nowadays, though: Stick to digital, physical only for stuff I LOVE. Because being physical only has left me with a LOT of stuff where I go "well, it's not BAD, but I probably don't need to own it physically... But then I can't recoup my money by selling it, but it's taking up space, but selling it is hardly better than just dumping it to get rid of it..."