The Accura has an aluminum alloy frame vs the stainless frame of the Apex. As a consequence, the Accura is a bit lighter overall.
The Apex barrel is removed via a pin like the Encore/Contender rifles, the Accura barrel is removed by only removing the forearm (like a Huntsman/Sidekick).
The Accura comes with iron sights, the Apex comes with a scope base.
The Accura trigger is not adjustable but is light, crisp, and NICE! The Apex trigger is adjustable over a fairly narrow range (mine is now at 2lb 10oz, low limit on that one), is also quite nice and crisp.
The breech plug on the Accura is simple and relatively inexpensive to replace (or buy spares). The breech plug on the Apex is more complex, removes easily without tools, and is almost certainly more expensive (unknown pricing at this time). The Apex plug did contain blowback even firing Swiss with heavy conicals - the Accura plug didn't do as well in that regard but excellent otherwise. Both shoot BH209 nicely but I would guess the edge would go to the Accura plug if there is an edge - no issues with either so far.
Cosmetics of the stock sets could be a factor but both shoulder very well. The Apex seems to balance a bit better but not remarkably so.
The ramrod for the Apex is more solid than the one for the Accura but both are good rods.
The Apex is a bit shorter overall, perhaps 3/4", at the expense of a bit of barrel length.
Both are very accurate rifles.
Have him shoulder both if possible. The Accura is more widely available while the Apex is in short supply at the moment.
I would expect the Apex to be somewhat more durable if he is thinking of a "lifetime" rifle, although I have no reason to believe the Accura wouldn't stand up to the test of time.
Cleaning, perhaps a slight edge to the Accura only because of the way the firing pin assemblies are arranged. The retaining screw on the Apex is a bit tedious while the entire cylindrical assembly screws out easily on the Accura. The Accura's is removed from an easily accessed open frame while the Apex must be removed from the hammer side (and the hammer does interfere just enough to warrant a ball-head hex of 2.5mm).
The Apex is considerably higher priced than the Accura and I don't know that it would be "worth the difference" for someone that wants only a muzzleloader. That would be a decision only the buyer could make.
ps: I intend to part with neither although I did sell one of my two Accura rifles to help fund the Apex purchase.