I'm looking at getting a M9 in a few months and the only thing that I would like to change is the plastic guide rod, trigger, and safety. Brownells has a Beretta steel replacement kit for it ( out of stock thou ) that I would probably get after a few months. My only worry is that the steel guide rod might care excess wear on the handgun compared to the plastic guide rod. Should I stick with the plastic guide rod or will I be ok to use the steel one? Thanks in advance for the help.

I don't think it will matter in the big picture.  Just lube it.  Yes, technically steel slide VS steel rod will have some wear, but really how much if you lube it properly?

I think you'll be OK with either rod.  There's nothing wrong with the poly rod IMO, and there may be some advantages.  All of them too small to worry about.  Mine have steel because that's what they came with.  No issues.  If they were poly, I'd have probably just left them poly because they work fine as well.  If you want steel, I don't think there's any problem with that either.  Just lube it and you should be fine.

The plastic was a cost saving measure. My 80's Italian 92 is steel.

I was told that a plastic guide rod was used becuase the metal ones would get bent and render the weapon unusable.

 
Yeah, but when you make millions of units, $0.25 adds up quick.

Good point. Post edited

So..what happens when a plastic one fails?

The gun will probably stop working?

Agreed. My old 1995 F150 had drum brakes, therefore the disc brakes on my 2013 F150 are a cost-saving measure.

It will be broken and have to be replaced.

As opposed to being bent, and the operator assumes he can rebend it and it will work.

I just bought the steel kit for my beretta M9 from Beretta USA. It is $70 and you can get 10% off by signing up with your email. Ordered it Monday night and it shipped on Tuesday. I am excited to see what it looks like when UPS finally gets it here. The plastic stuff all works fine, but I just prefer steel on a metal handgun and I like how the steel parts will wear over time with the rest of the gun.

As for the guide rod, I actually think I prefer the plastic. Both are good, but the plastic is lighter, one piece, and has relief cuts for sand/ grit. Also if it got bent somehow or broke, the broken pieces could not damage the slide. I am sure both are fine in the real world and most will likely never have a problem with either.

I replaced the plastic guide rod in my M9 with one that i made from grade 5 Titanium.  As light as alum. but stronger than steel.

I put a steel guide rod in my 92A1 first thing. Haven't had any problems or unusual wear. I had a plastic guide rod fail in a 226. The rod disengaged from the barrel and seized the slide. Had it been life or death I would of had a huge problem.