Well, with a mystery quilt we don't know if everything will trim down and work or not. If all parts are now made/cut and work with the square math (as opposed to rectangle math) it would be just fine to trim down and make them consistent. Sometimes it will, sometimes you think it will and then you cut the offending block in half and that takes out any flexibility you may have had.
I'd go with it as good enough if you can. I'm not impressed with my workmanship on my current project but nobody but me knows what the back looks like!
As I deal with my vision issues I prefer to make large and cut down for precision. Also, I work quite fast and slicing and dicing is easier for me than trying to get my eyes to work on slow and careful.
If I had to exchange blocks with other people, I would do them again. For me, it's rare I redo. One of my recent projects was quarter-square blocks made from pre-cut 6" squares. Yeah, most of them worked just fine but when I ran out of 6" squares and used 6.5" squares and trimmed them down I was much happier.