It can't be that bad since fpc has adopted some of it.
+=,. -= *= etc..
FPC hasn't adopted those. They are only supported for conversion purposes, and were never intended to be used in newly written pascal code.
To that I agree, but why never marked such use as deprecated... I once asked for =+ (first assign, then increment =++ as opposed to ++= )etc... which was refused. I think {$coperators on} should be - well - deprecated.
They are not complete and misleading.
On occasion I also misuse the feature, though.