I'll compare it to Bloody Victory: Sacrifice on the Somme by William Philpott.

Hart's was the first I had read on the battle, and as an introduction to the battle I think it's ok. However, I feel it has some major shortcomings (all of which are not present in Philpott's work). Firstly, Hart spends a lot of pages on the first day, I think it was about 100 pages. To be fair, that day has been seared into memory as an important day of signifigant loss, often begging the question of "what for?".

That's where Philpott comes in. His work is much more comprehensive, and shies away from focusing on the disasters of the first day to the detriment of literally everything else. For example, Hart pretty much entitely ignores French contributions to planning and execution of the battle (Philpott covers these topics in depth), doesn't talk too much about the Germans, and doesn't talk about the impact of the battle on the war, at home, and in the future. All of which Philpott covers.

Philpott also has a section on WWI and memory, which was great. On the whole, Philpott is a part of the "Revisionist" school of thought in regards to WWI, and tries to shy away from the whole "It was a waste" narrative, and instead looks at the Somme in context in an arguably just war of attrition. Hart looks at it through the old lens, "Lions led by Donkeys" and that it was a waste, and that the first day of the battle is what really mattered and the success later on don't deserve as much coverage.

I'd say Hart is an ok start on the battle, but there are certainly other books out there I'd recomend above his.