Really happy with my plates from Fancyplates - great quality, and I'm fussy.
At Halfords they assembled my rear plate by hand - the letters were placed in a kind of jig, but the perspex is static and the characters can move as the two sides are put together. The assembled plate was then put through rollers - more potential to move the letters.
The guy there said they were getting some 'laser cutting' system at some point which would presumably be better - maybe that's what Fancyplates do.