Every stick on plate is illegal and an MOT fail.
Every square plate on a non-import.
Every plate without the BSI mark.
Every plate with something other than an EU flag and GB.
Every plate with a slogan at the bottom rather than the garage who produced it.
Etc. Etc. All illegal.
Yet I haven’t had a standard plate on any of my past four MX-5s and I’ve never been pulled and I’ve never failed an MOT over it. Yet. Touch wood. Probably been lucky, but I’m also not alone with this so… And none of my plates have been ridiculously different, just a little bit smaller, stick on etc. I always go for standard font and spacing.
The further you get from standard the bigger the risk, and you can be unfortunate and come across a policeman or MOT tester who’s had a row with their partner that morning, but generally so long as the plate can be read by automatic plate readers (I tested mine at Tesco’s!) I’d go for what you like. Or you might find it a source of anxiety that you might get pulled, in which case I’d not bother because it’s a silly thing to be stressed about.
That said, if you do get pulled, don’t blame me!