Using a Romanised Japanes course to learn the language?

Several people have said Hugo Japanese is a very good, no-BS, grammar based course. I've flicked through it and it certainly looks good, however, there is absolutely no kana used throughout, it is purely taught with romanisation.

I have learnt Hiragana to a fair level, so if I read texts written Hiragana outside this course, should the fact its taught via romanisation not be too problematic?

The process of learning Japanese is 90% about learning Kanji.
I advise you to not use that book and get yourself familiar to Kanjis as soon as possible, unless you want to be illiterate in that language.