At my table we have yet to use free archetype or dual class. There are definitely free archetype enthusiasts in the community (and power to them!), but I'm not convinced it's quite so ubiquitous.
I think Ascalaphus has the right of it: unrestricted free archetype is at its best in smaller groups who are missing roles or to thematically reinforce a campaign with a pre-selected list of archetypes.
Is the flexibility within class suboptimal/flavourless? Perhaps. There are some levels where classes don't get any exciting or competitive feats, that is true, but there's nothing precluding you from investing in an archetype without the variant rule. If it's a concern of impactful feats, free archetype won't remedy that either; there will always be an optimal option for what you're building towards, whether it's a choice between two options or ten.
If I were to implement free archetype at my table outside of a thematic campaign or a small group, I would probably restrict it to low level feats only: free dedication and the first two feats at or below level 8, for example, and perhaps veto some of the power archetypes that can accomplish their goals in only a couple low level feats (Blessed One and Champion, amongst others). It gets around the concern with getting level 10+ feats for free and helps mitigate the whole erosion-of-niche issue.