Hiring is cheaper for a single one-off. Buying is cheaper the moment you run events more than a couple of times a year, because a hire fee is paid every event while an owned bench is a one-off cost that works for years.
The maths is simple: total up how many events you have this year. Past two or three, the repeat hire fees overtake the cost of owning a LED Bench Light Box at £199, and you end up with nothing to show for the spend, versus an owned bench that turns up ready each time.
The other factor is branding: hire gives you a blank bench, owning lets you put your logo on it. For anything repeating or branded, buy. Plan yours on a free mock-up.