It’s very effective, just tedious. That was my usual method and when they were bad, I was out 3 to 5 times a day. Drowning them in plain water takes them too long to die which seems cruel. Plus like you said, they can climb on others and escape.
I’ve never had them climb out, and the yard is so large that I couldn’t stomp them, because most of the gardens are too far from a hard surface. It’s no more cruel than poisoning them, imho.