Katakana "タ" (ta) is almost the same as kanji "夕" (pronounced "yuu") that means "evening". There are more cases of similarities. Katakana "エ" (e) is the same as kanji "工" (kou) that means "craft" or "work" Katakana "カ" (ka) is the same as kanji "力" (ryoku, riki, chikara) that means "power" or "force" Katakana "ニ" (ni) is the same as kanji "二" (ni) that means "two" Katakana "ハ" (ha) is very similar to kanji "八" (hachi) that means "eight" Katakana "ロ" (ro) is the same as kanji "口" (kou, kuchi) that means "mouth" They are indeed confusing for learners of Japanese, but we do not get messed up because we can distinguish them by way of context and collocation in the sentence. Like in English, "1" (one) often looks like "l" (el) but English speakers rarely get confused.

You can normally tell just by looking at a sentence. I don't think there are many one-letter katakana words. Also, the context of the sentence can help you. パンダは口が大きいです。　Ｐａｎｄａ　ｗａ　ｋｕｃｈｉ　ｇａ　ｏｏｋｉｉ　ｄｅｓｕ．Ｐａｎｄａｓ　ｈａｖｅ　ｂｉｇ　ｍｏｕｔｈｓ．　”Ｐａｎｄａ　ｗａ　ｒｏ　ｇａ　ｏｏｋｉｉ　ｄｅｓｕ,” just doesn't make sense.

Yep, like nobody in America thinks A1 sause is made of aluminum, well, I hope not...