The downside, however, is that at £34.50 the cost is steep and your author isn't sure it is worth that much, even though you do get to learn some interesting titbits along the way, and even get the chance of spotting a 'ghost station' or two along the route.
For the money, the tours are also private, held in small groups, and they run whenever you want, beginning at Farringdon and ending at Westminster. For real enthusiasts there is also a six hour option which costs £79.50, and doesn't include lunch because they 'like to let guests choose exactly what they would like'. In truth these tours are both prohibitively priced for anyone but the most ardent cash-rich underground fan, and your author suggests you might be better off buying a book and doing it yourself.
For more on the tour, see http://insider-trends.com/london-underground-tours/ or to book email email@example.com.