These commercial rubber dumbbells are far superior to traditional hex dumbbells for a variety of reasons: superior knurling, commercial quality, non-slippery rubber, single-unit assembly.
While people tend to lean towards the cheapest option for dumbbells, it is important to realize fitness equipment is an investment. Purchase the best equipment bit-by-bit to avoid replacement. Often times people spend hundreds of dollars on mediocre equipment multiple times, rather than saving money in the long-run and purchasing superior equipment from the beginning..
While traditional hex dumbbells seemingly are adequate for most peoples needs, the knurling is subpar and has an inability to allow chalk to "stick" (problematic for intermediate and advanced lifters), the material often has a toxic odour, contains slippery rubber which is often perpetually greasy, and occasionally the ends can come loose (no matter which company you purchase them from) as they are not single-unit manufactured.
For those interested in gym-quality dumbbells at a reasonable price in 5-120lb, I highly recommend you spend the extra money and purchase these as they will last a lifetime.