These cards are great and well worth the price.
They are made from a high quality card which gained them a star.
They are very informative, giving several examples of words with each letter, and do exactly what they advertise which gained them another star.
They writing on them is clear and easily readable, very important given the characters they are showing, another star.
They are pocket sized so can easily be shuffled, carried around, stored away without any issue, 4th star.
They missed out on the 5th star though because of the accuracy of the mnemonic examples given. Several of them (around 6) require saying the mnemonic with an American accent which, although annoying, isn't itself a deal breaker. What stopped me giving the 5th star was the example given for the hirigana Sa (さ) which is pronounced like the sa in Sahara Desert. In their example they give the word Sob, as in crying, which by my pronunciation is more like sorry or So (そ). Even putting on my best American I can't make SOb sound like SAb and given the importance of getting the sound right in Japanese I can't in good concious give 5 stars when it has such crucial mistakes.
These mispronunciations are very obvious even from an early stage, given every kana has the A, I, U, E, O sound you'll soon be able to tell if a mnemonic is out of place and will be able to make your own (and to be honest I only find mnemonics useful for the first month or so before I just started being able to recognise them with the need).
So in conclusion, definitely buy them they are a great purchase but watch out for the mis-leading mnemonics.