Are the grab handles on cheap dog life jackets actually strong enough?

For light pool use, yes; for hauling a 70-pound wet dog out of a lake or onto a boat, reviewers and specialist subreddit threads strongly recommend a reinforced handle stitched into a load-bearing harness. This is a recurring criticism leveled at the cheapest vests, and one of the main reasons Ruffwear and EzyDog command their price premium in the consensus.