Got a gen1 full size 9mm that isn't meeting my accuracy requirements. Least accurate of all my pistols. Looking to replace the barrel with something significantly more accurate.  

Considering the Apex tactical, but I know it requires fitting. Are there any other decent options for improved accuracy?

AFAIK, the APEX is the only one that actually improves accuracy.
The reason for the inaccuracy is due to the early unlocking of the barrel, this can only pretty much be solved by the semi-fit nature of the APEX barrel.

The fitting isn’t that difficult. But the jig and file and do it yourself after watching the videos online.  I am super impressed with my 2.0 after replacing the barrel and I don’t get super impressed with much these days.

Same here.  The Apex file to fit barrel made a really noticeable improvement in groups in my 2.0 5" 9MM.

I've bought barrels from other companies that didn't make the M&Ps shoot better.  Only the Apex (only bought the one) worked to improve one of my full sized M&Ps.

Maybe I got lucky on mine, I only had to remove a little metal from the rear of the barrel hood.  My 2.0 is sloppy enough inside that no contact is made up front or farther back on the barrel.

OP, I think I understand your "need" for nice groups.  I've sunk some money into my M&Ps trying to make them shoot better.

One more thing, OP.  Don't know if it holds true for the 1.0's or your 1.0, but the best shooting ammo I've found for my 2.0 5" 9MM is the Winchester 124 grain FMJ NATO ammo.  I've been trying to load up some 124 grain hollow points with a similar velocity but haven't found the right powder/bullet yet to get me there.  If you can find some, give it a try.

Maybe I got lucky, or the compact is a different beast, but I have been satisfied with the accuracy of my 9C. Even outshot a few HK's and Sigs at a local class in an impromptu competition. Only reason I would swap my barrel would be to run a threaded barrel with a comp.

Standard experience, the 1.0 9c typically shoots much better than the 1.0 9fs.

Get the Apex SDI. There’s no point in buying a different drop in barrel.

I have 5 semi drop in barrels. All are great.

We have two 1.0 9MM Shields that outshoot my full sized 1.0 and 2.0 9MM and .40 M&Ps.  Seems crazy to me that a tiny pistol like that would outshoot the full sized guns but both of them do.

That's what I figured. Looks like an Apex barrel is in my future.

Wow.  I have had many days where I have shot better with my shield vs a 1.0 FS.  I wondered how that could be.  Never thought it could be the mechanical accuracy of the barrel.

Been thinking of getting an APEX barrel for me 1.0FS. Accuracy is good enough for combat type shooting but it's nowhere near as accurate as my 2.0FS.

Not sure if any still remain, but Agency Arms had some 'blemished' barrels on their website for under 130$... I ended up with a pile of them for several M&P variants.
All were vast improvements on stock accuracy.

The only blemish I could find was a tool mark or two in non-critical places.

KKM

I haven't experienced any accuracy issues with my FS 1.0 .40

Apex does seem to be the go to for S&W upgrades

Op, I have very gently used storm lake I think, m&p 9mm barrel just laying around.
Wanna try that and if it works, we could work something reasonable out?
It prolly doesn't have 200 rounds fired through it.
Non threaded, standard length.