Those are some of the better RTL-based sticks you can buy so yes they'll work fine. As for trunked system monitoring while it might technically be possible to do that with just one (meaning it'll hop from the control channel to the voice channel and back as required) it's vastly more efficient to do that sort of monitoring with two tuners where one can be dedicated to monitoring the control channel for data as required and the second one will hop the voice channels as needed.
So yeah, get two of 'em, absolutely.
And if you don't have any SMA connector antennas or cables presently then you're going to have to get that as well - I would recommend that you get the version of those RTL-SDR blog sticks that do come with the antennas so you can at least know they're working before committing to purchasing more expensive antennas (or making your own which is what I almost always recommend nowadays, it's not that tough to build a small workable antenna for given frequencies or bands). The antenna-included models of those sticks are about $5 more but again it would mean you can get to work immediately when they arrive. They're not the greatest antennas in the world, no, but they will work for testing purposes more than not having any antenna at all and they may prove to work out great for your exact purposes.
