At first, I found this useful. It helped me to understand things clearer, and it explained things such as consonant gradation in a more extensive way than Teach Yourself Finnish. At first, I would have recommended it...
But lately, it's just confused and infuriated me to the point where I can't be bothered learning Finnish anymore. Perhaps it's just me, but I find it uses too many complex sentences when trying to explain things, which is even more confusing, because it takes one confusing idea, and explains it with loads of confusingly-used terminology (Not that I'm a dunce...I do know a lot of the terminology such as Nominative, postmodifiers, intensifiers, etc...) which means that by the end of the paragraph I want to tear my hair out.
It's also annoying that it lacks simplified explanations or ways of remembering things. For example, I was trying to study sentence order earlier, but instead of having a clear 'Adverbs go in Time, Manner, Place' order, or 'In 'että' clauses, verbs go to the end of the clause' (For example), it went off on explanations that are hard ot pay attention to, much less understand.
What makes it worse is the lack of exercises, which would clarify things better than those run-on sentences. I know that I cna use my Teach Yourself Finnish for this, but the grammar in that book's spread out all over the place so trying to find one particular piece is difficult and boring.
However, there's no other Finnish grammar books available in English (That I know of), so it's just one tha thas to be bought and wept over, I suppose.