Just picked up the Lionel Legacy Missouri Pacific FA-AA set from my LHS (Forum sponsor) this weekend. Both this set and the sister Alco Demonstrator set are on sale for a very good price.
Each unit is powered, which is a first for me - all the other AA sets I own have one powered unit and one dummy unit. I set up each unit with its own engine id# and then lashed them together as one unit using the "Train" set-up. First impression is that they run very smoothly together with no hesitation or jerkiness at all and all the Legacy features, including smoke, work well.
Although they will run down to O-31 (my layout is predominantly O-36), it looks like Lionel has shortened the drawbars a little to tighten up the coupling distance between units for a more realistic look.
The rear foot steps on both units (4 in all) come out-of-the-box bent outwards. According to Lionel, they are made this way on purpose to allow coupler/pilot clearance on tight curves.
The 2019 catalogue shows the engines with matching blue side-frames and mine came black - I know, Lionel has a disclaimer that they do not guarantee that the finished product will look exactly like the catalogue picture, but it was still disappointing. I will probably end up painting them silver, since matching the blue will be difficult.
I haven't seen enough real-life pics to say whether the colors on these engines are correct or not. I've seen some post-war MP engines by Lionel at various train shows and this blue seems a little darker than those. I would say the sheen is about a semi-gloss.
I haven't tried running them with any rolling stock, but with both units powered by dual motors, I don't think there will be any issue with them pulling a long consist.
(Edited parg. 4 to conform with Dave's comments.)