Iv read the elander is the way to go, but my question is reliability.

I'm seeing the elander mags in 4, 10, 17 and 24 rd.

Is one size more reliable than another?
Pros and cons?
Best prices?

I have all sizes of E-Lander mags except the four round mag and they have been gtg.   Alexander Arms sold rebranded C Products mags until it was taken over by ASC.  AA never sold the 15 round mags that are the same size as a 20 round 5.56 mag.    The 15 round mag really could’ve benefited from a curved body so the fatter 6.5 Grendel cartridges would’ve stacked better.   I have three of the early C Products mags which are advertised at 15 rounds but only hold 14 rounds.   All my C Products and ASC mags hold one round less than the advertised capacities.   I normally only load ten rounds in my 15/14 round C Products mags but I had a couple of malfunctions early on when loaded to full capacity.    Whether this was because the mags were new I can’t say.   I normally shoot off the bench with this particular AR-15 and never really load more than 10 rounds when target shooting for groups.

I’ve had to clean the interior of my ASC mags as they had a gummy  substance inside the body.  I had one 24 round ASC mag which failed to feed from one side.  Once I tweaked the feed lip the mag has been gtg.   Unfortunately a few bad mags have slipped out by all 6.5 Grendel mag manufacturers.   All new mags I’ve purchased have been E-Lander since they hit the market.   I like the 17 round E-Lander mags the best, good capacity, less weight and bulk plus work off the bench.

I have not purchased any of the C Products Defense 6.5 Grendel mags.    The curved 28 round CPD and 10 round CPD mags generally get good reviews.  I suggest you order mags from a vendor with good customer service in case you get a bad mag.

I’ve found the mag springs to be very stiff on new 6.5 Grendel mags.   The E-Lander 6.5 Grendel mags have the stiffest springs when new.  I suggest you load your 6.5 Grendel mags to capacity and let them set loaded.   This seems to accelerate the wear in process.   Once worn in my 6.5 Grendel mags function reliably.

The mags I don't think I've ever seen failures with are the 25rd CPD or older C Products mags.

The mags I've seen the most issues with are the 15rd straight mags that were never supposed to have been born, but they work if not loaded to capacity.

My main mags are Elander 17rd and CProducts Defense 25rd mags.