It's not all that rosy though re regularity. "si" is pronounced differently depending on ~whether it's in a loanword (compare silos and silnik). "rz" is sometimes two phonemes (e.g. in marznąć or mierzić, but surprisingly enough not in obmierzły).
Your guide is imo very helpful. I'd quibble a bit about "cz", because the way I pronounce "ts" is closer to Polish "c" than to "cz". (The way I think about "cz" is that it's a more plosive "sz", but am not sure whether that's a helpful way for people who don't speak some language with similar phonetics natively.)
@robryk @oldladyplays I always provide “cheshire” as the closest english approximation of both cz and sz, by pure chance.
then again, it’s a british place name, so you can’t really tell how it’s pronounced anyway, back to square one. /hj