Also: from having been through the patent process a bunch of times: does this make it "harder" to obtain a patent by eliminating the ability to sell the invention under NDA before filing? I remember this being part of the M.O. of building, selling, and then patenting technology at companies I've worked at.

The "First to" is speaking about what happens in an interference proceeding between two patent applicants. What counts as prior art is largely unchanged— it's arguably even strengthened a bit (as a dishonest player could previously get away with more backdating of his lab notebooks).

Third party— that is, not derived from the applicant's work— public practice (which is pretty broad, including publication and use in a product available to the public) is an absolute bar to patentablity. After one year the "not derived" part goes away and even the applicants own publication (and work derived from it) constitute prior art. (this was all also the case before, though the details a somewhat subtly different)

To quote the statute:

(a) NOVELTY; PRIOR ART.—A person shall be entitled to a patent unless—

(1) the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention; or

[...]

(b) EXCEPTIONS.—

(1) DISCLOSURES MADE 1 YEAR OR LESS BEFORE THE EFFECTIVE FILING DATE OF THE CLAIMED INVENTION.—A disclosure made 1 year or less before the effective filing date of a claimed invention shall not be prior art to the claimed invention under subsection (a)(1) if—

(A) the disclosure was made by the inventor or joint inventor or by another who obtained the subject matter disclosed directly or indirectly from the inventor or a joint inventor; or

(B) the subject matter disclosed had, before such disclosure, been publicly disclosed by the inventor or a joint inventor or another who obtained the subject matter disclosed directly or indirectly from the inventor or a joint inventor.