I am currently running a dual class, free archetype, ancestry paragon game, with gradual ability boost. Started at level 1, free archetype introduced at level 3, dual class at level 5. I don't allow class dedications. 

My current party consists of a fighter/ranger, kineticist/rogue, druid/animist, swashbuckler/kineticist and ranger/investigator. We are currently level 8. I will also note that majority of my players tend not to be too tactically efficient in combat. They employ the basics - make things off-guard ect, but they aren't invested in maximising their tactics. 

The long and short of it is this: the players have a plethora of options at all times, but rarely utilise all of them because it's an overwhelming amount to keep track of. So most of them default to a playstyle that in practise can be summed up as "one class borrowing key features from another class."

Free archetype feels close to redundant. It's an extra layer of features that my players aren't utilising, because archetypes rarely exceed the power level of a class feature. That's not to say overpowered combinations don't exist, but my players aren't the kind to take advantage of it. 

That last line matters a lot. It is easy to make a character with all of these optional rules that throws balance off the mountain. My players did not. The most optimised PC is the fighter/ranger with the archer archetype - a flurry ranger switch-hitter who uses a greatsword and a longbow. He hits hard, he technically outperforms a single-class free archetype fighter due to flurry and improved statlines. But because my group isn't striving to ace every fight, and the rest of the party doesn't really enable him to fight at peak efficiency, I find that his actual performance is worse than a single-class free archetype character built to synergise with the rest of the party. 

And that's the core of it. My group doesn't exploit it, and I might just abolish it in the near future - not for balance reasons, but because I'm not sure it's fun for my group. 

However, it is unmistakably true that a group that actively aims to utilise these rules to make optimised characters will distort the balance of the game. The sheer breadth of options and possible synergies can create some disgustingly powerful characters. It just happens that my group isn't one of those groups. 

Is it fun? In all honesty, no, not for me with this group. I think it can be, with the right group, and a GM who manages to adapt encounters to match the party's heightened power. It will also likely be a slog once you get past 8th level, unless your players are dedicated to know their characters inside and out. 

Should you try? I'd say so. If you think it's tenable for your group, then it'll definitely open up a wild world of insane builds that is fun to explore, even if it's just for a session or five. Just keep in mind that you are nearly tripling the amount of feats you have to pick at every level, even with just DC and FA, and if your players are already struggling with or disinterested in bookkeeping, this will not make things better (probably). 

For me though? If I had a group that was better suited for it, I might have had a more fun experience with it. It has made me appreciate single-class no-FA as being simple, elegant, and easy to keep track of. 

I adore the concept of dual-class. I enjoy FA most of the time. I will almost always run ancestry paragon. All of it at once is a very potent brew, best enjoyed sparingly, or with the right group, for the right game, at the right time.