I don't shoot my .458 much so I never bought a bunch of mags for it.  Now  since I don't have anything else I am panic buying, I think I want to buy a few mags for it.  I have short mags for it, what I would like to find are "standard size (30 rnd 556)" length.  I remember when I first got it, pmags were a pain because of the ridge in front, so I just used GI aluminum 20's.  

So, whats the current favorite for 458?  Ideally, is there someone selling one with a single feed follower installed that requires a minimum of tinkering to make work?

Lancers seem to be a favorite

Tony Rumore has followers

https://tromix.com/product/center-feed-followers-for-lancer-mags/

You don't need followers unless you state dictates that your mags cannot function properly with any other caliber.  Such as your state requires your magazine to only hold 10 rounds of .458 SOCOM and cannot hold anything else.  In that case, the sled follower prevents the magazine from operating properly with 5.56 ammo because it will auto dump the last two or three rounds in the magazine all at once and jam up the rifle.  But if you live in a free state, don't waste your money on the followers.  Just get any quality 5.56 magazine but P-Mags are still a no go with the .458 SOCOM with many of the bullets used in it.  P-Mags will work with some bullets, such as JHP because you don't seat to the full 2.250 inches, but with spitzers like the 250-300 gr. Monoflex and TTSX bullets, the rib in the front of the magazine screws things up when seated to full magazine length of 2.250 inch.

The mags I use almost exclusively are Lance AWMs, 20R and 30R, but I also have had no issues with just about any 20-30R standard aluminum magazine.  If it will work for the 5.56, it will work with the .458 if your barrel extension is not jacked up on the barrel from the maker trying to reinvent the wheel.  If you have a quality barrel, like one from TROMIX, TJ, SBR, SSK, or RRA, it will work with completely unmodified 5.56 magazines.  The only thing you might consider doing to any magazine is cutting the half moon in the front of the mag so unloading unfired rounds is easier or if you are shooting very large meplat bullets.  You don't even need the half-moon cut if shooting spitzers or RN bullets.

Love Lancer 20's for shooting at the bench.  Have a few Lancer 30's for more "dynamic" shooting.  A couple of em have the extended base pads too which increases the capacity by two to 13+1.

No need to change followers too.

+1 for Lancer AWM. Others work but I bought a bunch to use for .458 SOCOM. Haven't tried the extension, 13+1 would be cool.

Just grab some aluminum GI mags too.

Lancer 20R Blem

This is what I picked up for my 458. I thought it was a decent price and looking at them, I have no clue why they are blend.

https://www.primaryarms.com/IsInStock+false?order=onlinecustomerprice:asc&keywords=lancer%20magazines

Primary arms doesn't like links...

I'm brand new on here, just building up a 458 SOCOM now.  Swung by my LGS and bought a couple of the Lancer mags thanks to the info given on here.  They had a bunch of ammo in stock too, so I got 4 boxes of the 350 grain FMJ-FN and two boxes of 300 Ballistic Tips.