I commented on this film a while back in another posting. I was able to read the script last year...right before they went into production. I liked that, in the version I read, all of the characters were based on real people...no composites, etc.
I also saw END OF THE RAINBOW, with Tracie Bennett, and while this film covers the same period in Judy's life, it is no END OF THE RAINBOW. It's not as over the top as all that.
In the latest, full trailer (released last week), I thought Zellweger's speaking voice, as Judy, had some of the inflections of the real Garland. Her singing, though, was not indicative of Garland in 1968-1969. I think the reason they let Renee do her own singing is that...had they chose to dub the vocals...the recordings from Garland's "Talk of the Town" engagement were pretty bad; both vocally and more important, technically. They were made on a portable reel-to-reel tape recorder and probably would never have been released were it not for the fact that Garland died within 5 or 6 months of the engagement.
I'm not sure the recording, which came out on a Canadian record label called Juno, is still commercially available (it was called JUDY. LONDON. 1969.)...but it really was not something you'd want as a remembrance of Garland. I remember one bit in the recording in where you hear a woman of the club's staff, offering a seemingly inebriated Judy some black coffee. Judy still had that great sense of humor when she replied condescendingly to the server, "No, I don't want a chocolate beer!"