Do not assume it matches the traditional broadsheet
This is the single most important thing on the page. Newspaper Club sells a traditional broadsheet at 380 by 578mm and a digital broadsheet at 350 by 500mm. Both are called broadsheets and they are not the same shape. The digital version is thirty millimetres narrower and seventy-eight millimetres shorter, a difference you will absolutely notice if you prepare artwork for one and order the other.
It is also the only Newspaper Club format with a ten millimetre margin rather than fifteen. So a designer moving between the two formats has to change both the page size and the margin, and neither change is one the software will warn you about.
What the smaller size is good for
It sits between a tabloid and a full broadsheet, which turns out to be a comfortable place for a lot of projects. You get the visual authority of a broadsheet page without a sheet so large it is awkward to handle indoors, and being digitally printed it works for short runs where a traditional press would not.
The page count runs in fours up to forty, which is double the traditional broadsheet's ceiling. If you want broadsheet presence and more than twenty pages, this is the only option in the Newspaper Club catalogue that provides it.
The margin is smaller, so be more careful, not less
Ten millimetres is not much. It looks like almost nothing on a 350mm wide page on screen, and the temptation to place a page number or a folio line just inside it is strong. Presses shift by a couple of millimetres as a matter of course, so a ten millimetre margin leaves you a genuinely narrow tolerance.
The sensible habit is to treat the stated margin as the absolute limit rather than the target. Keep body text a few millimetres further in than you are required to, and reserve the last few millimetres for things you can afford to lose.