Is a vehicle history check worth it?

For most used car buyers, yes. The check typically costs a fraction of what you stand to lose if the car turns out to have outstanding finance (which the finance company can reclaim from you, even if you bought it in good faith), is stolen, or has been written off and poorly repaired.

It's most worth it for private sales, where you have no dealer guarantee to fall back on, and for any car above a few thousand pounds, where the potential loss is highest.