Torpid's description of the generational differences in the Millennium series above is spot on. Further complicating things is that mags, etc. are not compatible as well between generations in many cases.
I had a first gen PT111 Millennium (not pro). It had issues which when fixed it became a fair shooter and mostly reliable. I did just trade it on a new 3rd. generation PT140PRO and they are totally different guns.
The new PT140PRO is well made, totally reliable (so far in 500 rnds) and has great features like light carry weight (18.7 oz.); fantastic single action trigger and very good in DA mode as well. Other nice features are 2nd. strike capability, Heine "Straight 8" sights, loaded chamber flag on the extractor. Also the grip is very ergonimical - the stippling and front/back strap ridges and ideally located as is the index finger dimple on the frame.
Looks like Taurus has worked out all the bugs on this line and the latest ones are very good guns in my experience at least with this one. The first gen. PT111 I had was a totally different gun . . . horrible trigger, uncomfortable grip, etc.