Given where the creators of this site are based I think some of those phonetic mnemonics only work if you imagine saying the words with a West Coast USA accent. 
I’m from the UK so they don’t quite work for me in the local dialect!
I do think the example sentences could do with improvement in some places so there are definitely some valid points in this thread and I’m sure it hasn’t gone unnoticed. But I don’t think the site is worse off for having them. Certainly when I was doing levels 1 - 20 I found it useful to practice my reading skills, even if I couldn’t successfully translate all of them by myself. I think I must be in a small minority of actually trying to read them!
Personally if you are in the early stages and want to try using them I would highly recommend installing this userscript (and in particular, the amended version of the script in the post I linked):
It replaces kanji in the sentences with hyperlinks to their WK page and an informative pop-up (readings, WK level) which appears if you hover over them. Also adds synthesised audio (which is certainly not always 100% correct but gives you some help.)