Lynam is clearly an expert and offers a wealth of strategies for arbitraging in sports, including horse racing (on which there is very little published material). He also includes many examples, and handy practical tips.
As another reviewer has already noted, however, straightforward arbitrage is becoming very difficult because of the growing number of arb-detecting subscription services, which has reduced arb lifetimes to less than 15 minutes on average. This has also made these "risk free" techniques increasingly risky, as there is a growing danger of failing to complete the arb before it disappears, leaving you with a conventional - and risky - bet involving large sums of money.
Only more esoteric arbs have much chance of working out these days, and while Lynam does include some of these, only readers confident in their algebraic abilities (and, increasingly, VisualBasic and Excel in order to program bots) will really be able to make this technique work for them.
In short, recommended - but be prepared to put in some hard work to turn the advice into profits.