I've only used it here and there (though have gone in-depth with a couple of passages), but it has seemed really helpful across the board. If memory serves, Wevers was particular that these were "Notes" (and not a commentary proper) compiled as a result of his work in editing the Göttingen Septuagint critical editions for the Pentateuch.
There's nothing like it, really--Brill has started its own Septuagint commentary series, and there is a volume on Genesis. But Wevers covers the whole Pentateuch, and often makes mention of the Hebrew, yet treats the Greek in its own right.
Not sure I can think of any drawbacks--it may leave some detailed analysis left to be desired, but these are "Notes," so it's understandable. Maybe someone else can weigh in.
In print I've rarely seen even a used hardback edition for less than $50; $35 or so for paperback, per volume. The pre-pub version elsewhere is under $150. Not sure how Accordance would price it, but $200 or under would be worth it, I would think.