I say wait for others who got one to start posting to see what they have to say about it. Not to mention trying to find one in stock.
I have 2 - Bronze Sniper models in .22 and .25, so I can give just a little perspective.
Actually I lied in that first line. I
had 2 M3's, but yesterday morning I sold my .22 cal here in the classifieds. I determined that
for my personal use it was too similar to my 2021 purchased MkII to justify keeping both .22's. And since the M3 has impacted (get it?) the perceived market value of the MkII so much, the M3 was the one which got sold. It is currently winging its way to a new owner in Philadelphia.
I will likely never get even close to using all of the capabilities of a gun like the M3 (or many of my other air guns), so my personal perspective is by no means universal. I like to achieve a proper tune for a smooth and relaxing shot cycle and accuracy, for a particular projectile, and then I pretty much like to leave my guns alone and just shoot them. I don't (yet?) compete. I don't particularly hunt, although I will deal with certain ground squirrels who are destroying the safety berms at our range. And, although I have dabbled with shooting some slugs and hybrid slugs, I still shoot probably 98% pellets.
The M3's are so new that I would imagine few shooters have even put enough pellets through them to get them through break-in. I know I haven't. I shot less than 150 pellets through my .22 before I sold it, and due to some questions posted on this board, I may have shot 250 pellets through my .25 so far. So the regulators in my guns haven't really even settled in yet to the point where any significant adjustments should be made.
And since they are so new, we haven't really seen whether FX's intent of providing the second regulator to prevent reg creep inherent in a single regulator system, and further flatten the shot curve will really come true. One thing that we have seen, mostly in Mavericks and a little in M3's so far, is the slower plenum refilling due to the interactions of the 2 regulators. I am pretty sure that this can be tuned out and will become a non-issue. OTOH we may also find some competition speed shooters will not be trading in their MkII's for M3's immediately.
The M3 is definitely an upgrade over the MkII. The cocking lever is noticeably improved, and the Micro/Macro wheels are very effective and easy to use. When I think about the progression of tuning the FX air guns I have owned, this company is nothing short of true genius:
1) When tuning my Boss or Royale it was great that they had an adjustable regulator and hammer spring, but it was necessary to disassemble the rifle to tune it.
2) Tuning a Crown or a DreamLine rifle now gives us the externally adjustable regulator and hammer spring. After tuning a Crown it is pretty difficult to go back to tune an earlier model rifle like the Royale.
3) Tuning an Impact is another step-up improvement over the Crown as now you don't have to remove the stock in order to fine-tune the hammer spring tension. Yeah, using that little hex key and only being able to turn it in small increments is a PITA, but at least I don't have to have a stockless action sitting on my shooting bags while I chrono the adjustments I am making, like on the Crown. After tuning an Impact it is pretty difficult to go back and tune a Crown.
4) Now we have the M3. Tuning it has become even easier with the sensible (single lobe cam) Macro wheel (something FX probably should have done from the beginning instead of the dual lobed 1-2-3, A-B-C hammer spring wheel) and the Micro wheel instead of needing to use a hex key. After tuning an M3 it will be pretty difficult to go back and tune a MkII.
So looking at the major changes to the M3 over the MkII Impacts:
1) Dual regs - time will tell whether this provides better, more consistent performance over the AMP reg in the MkII. Or maybe, more importantly, whether the dual-reg system provides better performance over putting a HUMA into your MkII, which can be done at a fraction of the cost of selling your MkII and purchasing an M3.
2) Tuning 'system' - A definite improvement over the MkII. Much more important to one who regularly re-tunes their Impact to shoot different projectiles, etc. Nice to have but not so important to someone who achieves an initial state of tune, and then leaves their gun alone and just shoots it that way.
3) Larger Power Plenum - Will be of benefit to those who choose longer barreled M3's, and have to have the maximum power available for shooting heavy pellets or for shooting slugs. But not my particular use scenario at this time, so I'm very happy with the available power from my MkII.
4) New cocking lever - While very nice, it by no means obsoletes the cocking lever on the MkII. I'm a righty, so the easy ability to change the cocking lever to the left side of the gun has less importance to me than it will have to others.
5) 20 MOA built into the rail - Yes this is a great and welcome feature for when shooting at distances over 50 yards. But can also be achieved with adjustable mounts.
6) The other smaller improvements in the M3 - Yes they are nice, but none of them 'obsoletes' the MkII, or makes the older guns any less fun to shoot as compared to the M3.
If I knew then what I know now, I would not have purchased my M3 in .22 cal, already having a similar (600mm instead of the Sniper's 700mm barrel) MkII. But I neither lost nor made money on the sale of my M3 so I got lucky in having been able to try one side-by-side and make the decision as to which one to keep.
So the M3 has some immediate tangible improvements over the earlier Impacts, and over time we will find out whether the other changes to the gun really pan out. The effect of the M3's launch on the perceived value of pre-owned Impacts seems a bit over-blown to me. For many shooters the M3's updates by no means justify the cost of selling your old Impact and upgrading. However to other shooters who want to wring all possible performance and power out of their guns (likely a rather small percentage), the M3's updates will be more important.
I think that I am going to like my M3 bronze .25 cal sniper a lot. But this is also my first .25 cal Impact, so I don't have an older model to compare it against. While many MkII and earlier Impact owners seem upset with FX for releasing the M3 and 'obsoleting' their guns, I have shot them side-by-side and don't feel that way at all. I still love my MkII and could care less that it is no longer the latest model. And my little .22 MkII compact - Well it is likely my favorite of the 3 Impacts I now own. No, I won't be selling it and upgrading to an M3 compact (even though I saw that Tony at TalonTunes had some of those in stock yesterday...

)
Just one M3 owner's perspective.