What's directly verifiable
HelloChinese's own website makes no mention anywhere of Traditional Chinese, Taiwan, Zhuyin, Bopomofo, or even Simplified Chinese — checked directly across its full marketing copy. For an app whose entire product is teaching Chinese, that's a real gap in the messaging, not a minor omission. If Taiwan-specific teaching were a headline feature, it's the kind of thing a course would lead with.
What's reported, and what isn't
Independent reviews report that HelloChinese added a Traditional-character display option to the app at some point — but no source describes this as a rebuilt Taiwan curriculum rather than a character-display toggle layered over Simplified-based content. And across every source checked, none mention Zhuyin support at all. Zhuyin (Bopomofo) is the actual phonetic system taught in Taiwanese schools — its absence from HelloChinese's feature set (and from every review of it) is a real, notable gap if Taiwan is genuinely your target.
Why a character toggle isn't the same as a Taiwan course
Flipping which characters get displayed doesn't rebuild the vocabulary, accent, or phonetic system underneath. A course built around Mainland-standard words and pronunciation doesn't become a Taiwan course by changing which glyphs it prints — and Zhuyin in particular is rarely part of any such toggle, since it's a genuinely separate system to teach, not a character swap. It's the same distinction covered in more depth in why Duolingo's Chinese course won't teach you Taiwanese Mandarin either.