Greetings from a former Joplinite (1982-1991)!
For monitoring the Jasper County NXDN system, which is a trunked system, I would recommend the Uniden 436HP (handheld) or 536HP (mobile/desktop) + NXDN upgrade. The reason that I recommend those radios over the Whistler models is that the Uniden models actually trunk-track the system whereas the Whistler models simply decode the voice channels. What this means is that by tracking the talk groups, you can be assured of following the conversation correctly. With the Whistler system of simply decoding the voice channels, you may miss responses even if you hold on a talk group. If you act quickly you can still get the NXDN upgrade from Uniden for an extra $30, but this will very soon jump to $60.
I have owned a Whistler TRX-1 but I sold it because I was dissatisfied with its complete inability to monitor any simulcast P25 trunked system and even some analog trunked systems.