My opinion of it?
OK, you asked......
The single z motor is a definite plus.
Effectively that is what I and others have done with our FT-5s.
I never liked the idea of dual motors and in fact I linked mine together mechanically when I first built the printer, so I have never even once operated it with independent motors and never intend to.
I would have converted to a single motor but I was unsure if a single motor could handle the required torque.
Since then it has been shown that it can, so if I were to do it again I'd go with a single motor.
I haven't had any particular issues with the melamine on mine, but then again I live in a relatively dry climate and I used load spreading washers at all the attachment points (to prevent crushing).
On the other hand, I know that many people have had major issues with it, so that is also a good thing.
As for the build plate, why don't you replace it with aluminum as others have done?
You don't need a solid plate at all.
You can do it with aluminum channels and angles just so long as you link the two Z motors together (there are many methods to do this) or convert to a single Z motor.
That is because it would be very easy to get the two out of sync and bend things.
The change to a 24 volt supply is a solid and most welcomed upgrade.
It is a MUST in my opinion.
It allows the load current to the build plate heater to be reduced to safer levels (assuming that you don't just bite the bullet and go with a mains-powered heater).
At least as importantly however, it allows the motors to run much better.
Quieter, faster, smoother, cooler, there is no down side to it and no cost penalty for it.
It is inexcusable that they didn't do this from the start.
I can't tell from what I have seen if they have upgraded the Z stop switch bracket or not.
The original is basically unusable IMHO.
It was one of the very first things I upgraded on mine.
The Y stop is not much better in that regard, but at least it doesn't drift constantly like the Z stop does.
I also can't tell if they have done anything about the ventilation for the electronics cabinet or not.
That is also a major problem on the original kit. Seriously!
I upgraded mine to have an 80mm fan and exhaust grille in the rear hatch cover.
Everything runs nice and cool now.
Along those lines, they need to offer a part cooler, even if it is a paid extra.
I finally added one to mine and it really helps when printing in PLA.
I do wish they had changed to a graphical display.
It is literally only $5 more and is far, far nicer to view and use.
However the original is perfectly usable and so I would chalk that up to personal preference.
I understand the price point that JF is trying to maintain.
I get it.
But if a $50 added option tier were offered to have a graphics display, a better Z stop, upgraded cooling fan, a part cooler, etc, I would have gone for it without any question.
The 713Maker parts are cool, but I gave up ages ago buying anything from them and went a different route entirely.
Try RobotDigg instead.
They have quite a few aluminum parts such as corners and tees.
Or, believe it or not, just go to Home Depot or Lowes or Ace and buy Stanley steel corner and tee pieces.
Yes, they do sell them in the hardware section.
They will work just fine.
You might have to drill some holes in them, but no big deal.
The Anycubic is cute.
I hope it works well for you and I hope I helped.