Poking around for simple upgrades, I want to try a tungsten guide rod for my gen3 G19 (well, a G23 with 9mm barrel).  

Glockstore.com has them in stock with options of 15, 18, 20, and 22 lb springs.  

Most of my plinking ammo is 115gr, defensive ammo 124gr.  

How careful do I have to be on spring weight? Will they just effect recoil, or could they potentially result in an unreliable gun that won't cycle?

Is this a competition pistol, range toy, or your life depends on it?

Are you troubleshooting an issue w/ the firearm?
Are you trying to gain a certain advantage?
Just curious as this isn't the logical way to a systemic approach.
Why do you want to try one if you're unsure what the end results are?

If you can shoot a 1.6S Bill Drill it may help you minutely.  If not, don't waste your money.

You can add more weight with a weapon light.

Fix it 'till it's broke.

OP  
The idea behind the tungsten guide rod is to add weight forward to improve recoil control. Unless you are a serious competitive shooter you won't notice anything, and most serious competitive shooters won't notice much if anything, either.  Steel guide rods make more sense and are cheaper, to reduce the chance of a plastic recoil rod breaking, which does happen, ask me how I know.
You probably wouldn't need to change the springs with a replacement guide rod of any type since the guide rod isn't part of the reciprocating mass (eg Glocks).  
FWIW, tungsten guide rods are prohibited in IDPA since they are heavier than stainless steel.  They are legal in USPSA as long as the gun is within overall weight limits for the division.
(edited for typos)

Like so many mods /aftermarket parts the number one reason they exist is to make money for the seller.

A MAJOR pitfall is that often times mods and aftermarket parts ( no matter how seemingly innocuous) will turn a reliable gun into a jam o matic

As implied above, most mods will give a VERY slight advantage in limited circumstances for shooters already at the top of the game, but no appreciable difference for the regular Joe.

Put another way, I see a lot of people trick out guns that think this will circumvent the need to master the fundamentals which is obviously false.

I also say give me the best quality modded to death gun optimized for a specific type of use, then give a master class uspsa guy a high point, and it is a safe bet they will still shoot better than me!

I resemble that remark.  I tried to turn a G35 into a Limited gun.  I don't think it ever finished a match without a malf.  Broken skeletonized firing pins, feeding issues with extended mags, light striker spring not popping primers, etc.  Bought a 2011 and never looked back.  Now that thing RUNS.

Yep.  In addition, I think that particular gun was possessed.

My only experience with one is that it made the gun less reliable. I took it out and put and an OEM guide rod back in. I really don't have any desire to ever try one again.

What is the goal here, OP?

I have no use for them, in my own use cases.

Sounds like a waste then. Glad I didn't dump any money on it!  

That is a thing, ya know.

A lot of stuff out there is gimmicky, little to no advantage or gain, or stuff many of us wasted money on and know from experience it is a waste.

The Tungsten(W) guide rod is what I would call gimmicky it does add some weight out toward the muzzle but not really a significant difference.  If you are trying to play around with spring tension you can accomplish it with a stainless steel guide rod and it adds marginally a little less weight than the tungsten.  But also changing spring weights can bring it's own host of issues by not matching it to the ammunition or properly adjusting the striker spring throws off the spring balance and can cause malfunctions.

I am not going to tell you not to do it but it is my opinion they tungsten guide rods are a waste of money unless you are going all out for building a range race gun where the focus is on speed and not life or death reliability.

I have the Jentra Tungsten G5 guide rod for my 34 with a 15 lb recoil spring and have had zero issues over a few thousand rounds using it.

That said, I don’t think it’s worth the price.  The biggest benefit is the lower weight recoil spring which you could accomplish with a steel guide rod for 1/2 the cost (or less). And you could do so with a captured system that is easier to remove/replace when cleaning your gun.

I have a captured steel guide rod in my G4 19 clone and will probably do the same for my 34 at some point.

I think it would make more sense in a 34 / 17L because you now have enough length to get a decent amount of weight.

The Carver is 2.8oz, which is about 1/2 a WML. With a WML you'd have 7-8oz extra weight out front.

https://www.shootersconnectionstore.com/Gun-Parts/Pistols-Other/Glock/Guide-Rods/CARVER-Tungsten-Guide-Rod-Uncaptured-Glock-Gen-5-G3435

I doubt theres much increase in speed, but extra weight makes for a smoother / milder recoiling gun at the range, which is something I like.

it took me years to enjoy Glocks. I learned to enjoy reliability and mod-ability. I have done many alterations to many Glocks (and have a stock Glock, also) in 9mm, 10mm, and .45ACP. Tungsten guide rods are the most recent - though I have used other SS guide rods, different-weight flat wound springs and whatever other doo-dads companies sold. Usually did all sorts of mods at once without trouble shooting in between. The sum of my Glock issues have been a broken extractor (on a stock 17 or 19, Glock replaced...think I had to send them the entire slide, though), and on a recent PSA Dagger build (I know, not a Glock, but I used same triggers and other things - a mix of high-end (or 'comparatively expensive', whatever term you like) and cheap-o parts - a striker broke - not sure I even got one shot out of it - and I was getting...let's say 'an unacceptable experience' when I both pulled and released the trigger, which caused me to immediately dissamble to firearm and leave the public range I was on until I was able to fix this issue...which was incredibly simple to do. I like the advertised benefits of weight up front - and I believe I perceive the difference in weight when I shoot (I have them in a 19 Dagger and a 17 Glock OEM frame build). I do not claim that they make me a better shooter or that they make shooting any easier. I haven't shot them enough to be able to parse what the changes I've made might each do. They satisfy my interest in checking things out, modifying Glocks, being a curious observer-shooter. SO they have some value to me, but as others have alluded to, not necessarily in ways that I would prioritize if my firearms budget was based on need or prioritized by improved impact on my consistency, accuracy, or speed when shooting. After-market parts sales is robust, though more a pain in the neck than I have time for except every few years, or when folks are scrounging for any usable parts so they can comlpete an assembly, as during Covid shortages.

I own many Glocks and the only one that has a Tungsten guide rod is a G21 that I bought used over 20 years ago. The original owner also installed a Trijicon adjustable rear sight.