Some observations I noticed and why I think training is better than buy another gun. (Still buyinh another gun though)
This was a basic Tactical Pistol Class. Nothing fancy, basic scenarios. Started with my EDC 1911. (S&W 1911ES). DId great. Kept a nice small group even during rapid fire. I was actually impressed with myself. After about 150 rounds, I started a scenario and noticed something wrong. Front sight broke off. Sh*&.
Took out the old trusty Glock 19. Did a scenario. Got a few misfeeds. Did another scenario. Got another few misfeeds. All 5 mags were not working. Loaded mags, stripped 1st round and watched as the next round slowely went up. Yes. I only brought my new Magpul GL9 mags. So I have no mags for the 19 that I can use. Brought out the trusty P229R with the P228 9mm slide. Finished the second half of the class without any other issue.
Good thing this was just a class. Learned I need to only use OEM Glock mags, my Sig can probably go through anything and I need a new front sight for my 1911. Don't know what happened there. Glad I brought several backup for the class, if not I would have left early and would not have been happy spending that money and going home early.

I am going to bet this is just like the CP mags.  Many arfcommers were felating the owner about how pretty the mags were and how quickly they shipped, but nobody actually tested them. When I bought a half dozen, most didn't work.  

The magpul Glock mags just aren't that much of a bargain over stock Glock mags that are proven performers. I still test every mag before I will carry them, but that is how I roll.

There is always someone at a class or match that brought backups.  All you gotta do is ask around.  I even loaned a gun to some folks at a CCW course that their cheap POS explode on them.

No version 1.0 of any MAGPUL magazine has ever worked reliable enough they did not have to come up with version 2.0.

I did a pistol class in November, using 10 Magpul and 5 ETS G19 mags, just to test them out.   Ran all brass, zero problems.  I carry OEM mags . . . but for training, these ain't bad.

Indeed bring a back up.  I bring at least one back up identical for the weapon I plan to use for the class.  

Other thing, stick with the weapon that got you there when you start taking the advanced class.  I have seen people take an entry level class a Glock, then decide to run a 1911 or something completely different.  They wonder how come they are having issues.  You are not running a platform you know.

I have had:
Broken frame on a 1911.  I did not notice for several months.  Got lots of malfunctions in class.

Weak hammer spring on 1911. Got lots of malfunctions, but the class was designed to have them anyway.  Got extra practice.

Weak springs in a Sig, was not sure I was going to make it through the class.  

AR blow up because of bad ammo.  ALWAYS WEAR EYE PRO!!!!!

Weapons gum up so bad in force on force training (using Simuntions) the next class I carried 2 weapons, and cleaned between iterations.

Rental weapon, Bolt gun, the bolt stop broke and I ripped the bolt out of the weapon.

When you're spending your money (and more importantly your time) to train, it makes good sense to have some redundancy in your gear because any machine can fail.

I think it's best to have at least two of the weapon that is your primary.  If something goes wrong, you can switch without really changing much else.

I bring loaners for attendees, and take back-ups to courses.

For pistol work, I just got out of 1911s after years of tweaking this, replacing that, "Oh you need to throat it to make it reliable, dontcha know."

After dumping thousands into extra work on top of $700-$1200 pistols baseline to try to make them work, I just gave up and went to Glocks and M&Ps.

I've never had a malf with an M&P yet, including taking one through a rain storm and mud.

I've used Glocks even in -30° C in the Arctic in the dead of winter for 2 or 3 days buried in snow, with full course curriculum and a heavy emphasis on clearing malfs.

Watched a CZ75 crack the slide stop shaft in those conditions.

Glocks caked in ice and snow kept chugging along like it was a nice summer day.

I do DM and Precision Rifle in the Winter in the mountains of Utah, where we always have sleet/snow, sub-freezing temps.  That puts a hurt on bolt guns pretty bad.

I'm a big fan of Cerakote to deal with conditions where you can have it applied without galling up your action.

For pistol courses, keep it simple and get a known quantity that has a reputation for reliability and commonality in the industry.

A course is not a place to experiment with a new firearm as an individual who is looking for training time value.

I personally send out a lot of homework/independent study before a course that includes zero, a reliability checklist, questions about the firearms, ammo, feed systems, aiming systems, holster specs if pistol work, followed with a quiz/test within 2 weeks of the course.

I can tell really quick who is serious about being there on morning one, and who is just riding on fumes that will need attention.

I love the attendees who are 100% in it to learn and get as much out of a course as possible, don't mess around.

This seems to be epidemic in the AARs I read.