As they say you get what you pay for spruce but you will only find out if something goes wrong and someone makes a claim against you how bad or good the insurance policy cover is.
Basic public liability is indeed not ideal cover to have for sure in this day and age. Insurance cover is also very specific to what activities are actually covered too so you might think you are covered when say doing a conservatory roof, gutter, solar panel clean etc but if it's not written into the policy doc you could find out the hard way you are not covered for that activity. Ladder usage is also very specific too as most don't cover over a certain height.
People tend to go for the cheapest basic cover which to be honest I think from my own experience is a total waste of time.