The handheld and panel-mount radios have very different missions.
The panel-mount radios have more transmit power, can be serviced instead of thrown away if they go bad, and are designed to produce performance good enough to be made available in certified versions. The receivers have filtering which attenuates all signals outside the aircraft bands, to protect against overload from nearby transmitters on other bands and frequencies. High-quality receive filters require more circuit board space than is available in handhelds.
The better handhelds are certainly not toys, but they make compromises to achieve small size and low current consumption. A handheld receiver section which covers multiple bands can be useless in an urban area due to overload from high-powered broadcast, pager, cell-site, police/fire, radar and other transmitters. The problem is especially annoying if you use a good, external antenna. When this overload occurs, it can "block" your receiver completely, so you may not hear the interference, but it could prevent you from hearing ATC.
The Sportys and JRL handhelds have cool features for the price, but Icom and Yaesu/Vertex appear to be of better quality, both receivers and transmitters.
If you run your handheld off the gyro's 12V system while in flight, upgrade from the standard nickel-cadmium battery pack to the optional nickel metal hydride pack. Ni-cads which are dischaged only partially before charging can lose much of their capacity in just a few charge cycles. If you do have ni-cads, let the radio run its battery down until the radio shuts off automatically before recharging to avoid this problem.