You would presumably still have to purchase separately additional boxes at their full retail cost (or obtain second hand ones). Something different from Virgin say which as part of their premier package (£48 pm) offer an extra HD box.
Whilst true, montycat, think of it in more basic terms.
£49 for a YouView from BT box plus £5 x 12 months = £109, plus the cost of a retail box at £250 equals a total of £359. And the eqpt is then yours to keep.
Whereas the Virgin offer you quote above is £48 x 12 months = £576.
And the eqpt is only leased, not yours.
So it's swings and roundabouts I suppose.