This would get you a better rifle than the Colt 6920 for under $700.
In what way is it better? Because its mid-length? because it is a LW profile barrel?
Is the RE on the one you linked to 7075? Most of what I see from PSA is not, hence their carefully worded description that it is "mil spec diameter." That is not better than what is on the colt. You can argue it is not a significant difference or that one could easily enough swap it out. But there is no argument that it is better.
Does the PSA you linked to have an H buffer tube like a Colt? With the midlength gas either will run but I prefer how a H buffer shoots and again I think it would be hard to argue that the carbine was better.
How is the staking on the gas key? I have personally had 3 BCGs from PSA. One looked great and the other two were poorly staked.
It will not be better in the sense of either resale value or liquidity vis-a-vis a factory complete colt.
Also you need to calculate for a rear sight.
It might be a fine gun that serves one's needs well, but I'd like to hear the argument that it is better articulated more thoroughly.
As to buying the cheapest stripped lower. I'm sure this is based on the mantra that a lower is a lower. I used to think that. Then I started encountering out of spec lowers. Some mildly so, some seriously so. Also some lowers really do have added features. One may not want them or may not believe they are worth the price. Do I think one is paying a pretty serious premium for the crusader cross on a gen 1 Noveske lower, I sure do. Is a lower a lower. Not in my experience. That said, yeah find the cheapest lower of a reputable maker and you will do generally do fine.
I do think the recommendation is likely to yield a good shooter and one could change out the things one did not like and be money ahead. I still think the patrol combos are better values in that one has a complete rifle not a mix master and the gun comes in at $600. It also generally comes with a rear MBUS. If you did a fire sale on the PRO for $300 you'd be at $700. It does take watching PSA's site as they tend to sale out and then re-list and the rifle they use changes and so do the options.