The Interarms Mark X is the commercial Zastava '98 Mauser.
Prior to Interarms importing them, Herter's did so and sold them as the Herter's J-9.
I have A LOT of experience with these. I had the "up-market" Interarms Whitworth Mauser in .270 Winchester and .300 Winchester Magnum. Standing at the counter of The Stockade in Westminster, CA, I couldn't decide which one was prettier, so I bought them both. The .270 Winchester was the more accurate of the pair (by a little, rather than a lot) and the more pleasant to shoot (by a lot, rather than a little). So, the .270 Winchester version is the one I used the most. When I write on here about filling 7 of my 20 elk tags with a .270 Winchester, an Interarms Mark X is essentially what I did it with, as all my Whitworth amounted to was a "tarted up" Mark X.
The Whitworth has the same fully adjustable trigger that the Mark X has. I had no complaints about the trigger, excepting that it incorporates a trigger-blocking safety and thus the bolt shroud has no provision for the three-position, striker-blocking safety of a military Mauser 98. Back then, there was an outfit that made Model 70 Winchester style safety conversions for 98 Mausers and I had my Whitworth rifles fitted with it.
The Whitworth had folding-leaf "Express" style sights on the barrel that the regular Mark X doesn't have, a different stock with a shadow-line cheekpiece and more lines per inch on the checkering, with a color-case hardened steel pistol grip cap. The barreled action was very highly polished and blued. It looked, felt, and functioned like a far more expensive rifle than it was.
If you inspected the things closely, you'd find the errant tool-mark or two, as you might expect from a "Commie Gun," but in general, in terms of quality of materials and manufacture, my personal opinion was that they shit all over the .30-06 Ruger M77's I had. When I bought mine, they were about the closest thing you could get to an "inter-war period" sporting rifle in something new. Forged actions with forged one-piece bolts; hammer-forged, hand-lapped barrels; milled steel bottom metal..... What's not to love?
The .270 Winchester Whitworth of mine was a one-minute or better rifle for five shots with a wide variety of factory and hand-loaded ammo. The .300 Winchester Magnum version I had was a lot more picky over the diet it got fed.
That's the good...... Now, the bad.....
The Herter's J-9 I had was in .243 Winchester. It was a rough-hewn thing that looked and acted like it was made by people who didn't give a shit about the end result with tooling that was well past its prime. The issues I had with it boiled down to cosmetic detail. I couldn't really fault it on the basis of function except that it didn't feed as smoothly as my long-action Zastavas did. Once I un-dicked the trigger that some prior owner dicked up by improperly adjusting it, it was an accurate rifle that was easy to shoot accurately. But, when I had the bolt open to load cartridges into the magazine, and looked at the lug raceway opposite the ejection port, I just couldn't keep something that crude. It isn't something I would have bought, with all of the errant tool marks in the action. It was given to me for free by an old lady who didn't want it in the house after her husband died. I had given her my phone number because I wanted to buy her Studebaker Avanti and she called me a few days later to see if I might want that rifle. I offered to pay her what they were worth at the time, with the idea that I'd get most or all of my money back, but the old lady refused and said she just wanted it gone, so I took it. I ended up giving it away to a guy I met at the rifle range who was looking for a rifle for his 14 year old daughter. I let the kid shoot it and she seemed to like it more than I did, and since it didn't cost me a dime to be generous, I gave it away.
I have encountered Mark X rifles that were riddled with tool marks like my Herter's J-9 was, and I have encountered a good many more that which, like my Whitworth rifles, were as close to perfect as one could reasonably expect such a thing to be, so I would say that Zastava commercial Mauser quality is, shall we say, "inconsistent" but if you get a good one, and the odds are in your favor that you will, it will be a good rifle that is more of an heirloom piece than something out of the modern discount bolt action bargain bin is.
Before 1992, when there basically wasn't a CZ 550 in the USA to compare the Interarms Mark X against, the Interarms Mark X was about the only game in town for people who worship at the controlled-round-feed action altar. Interarms sold the Mark X as a barreled action and also sold the actions sans barrels to the gunsmith trade, who used them as the basis for premium rifles.
I say that if you're interested in those Mark X's you've seen while buying your 7600, go back and open the actions on them. If you don't see a crap-ton of tool marks where they shouldn't be, look down the bores and if that looks good, check the muzzle crowns, and if that looks good, too......... Think about the money you're saving buying one of them instead of a new Portugal-made FN Model 70 Winchester, and the odds that either of those Mark X's will shoot as well, if not better, than a new Model 70 Winchester will.
I will say, too, that Academy Sports and Outdoors was selling Zastava commercial Mausers for a brief period of time, and the Cabela's in Rogers, AR had a bunch of them, too, and I have a lot of deep regret for not buying one when I had the chance, especially at the price point they were at. I generally don't regret selling a firearm when I sell one but I absolutely do regret deciding to sell my Whitworth in .270 Winchester.