Whilst it is true that in the case of Cantonese some tones can be misused without the loss of the comprehension in a conversion, and the non-native speaker will still be understood if the surrounding context is clear and concise, that is not the case with the low falling tone, which is the most unforgiving of all. Cantonese speakers are prone to get thoroughly confused when the low falling tone is substituted for a flat low tone or a low rising one. Consider 墳墓 and 分母 when the context is insufficient to deduce which word was actually meant; it is perhaps not the best example but I can't think of a better one at the moment.
> It's difficult for a non-native speaker to distinguish between "low rising" and "mid rising".... so just treat it as a rising tone. I'm a native speaker and sometimes I forget which type of rising tone a particular word is.... I didn't learn it that way, haha.
Most native speakers of tonal languages are not even aware of the fact their native language has tones. They don't think about it, they don't think about the tones. Tones are a concept for speakers of languages that do not have the tones in the first place.
The 5th and 6th tones are very close to two of the first four. If you pronounced them exactly the same as their nearest matches, Cantonese speakers would understand you.
The 7th, 8th, and 9th tones are basically very short versions of 3 of the first 4 tones. If you pronounced them the same, but just made the syllable very short, you'd be fine.
So yeah.... 4 tones. :-)