As a result of your antenna height and other factors, your actual transmitter power may need to be substantially more or less than the ten or hundred watt class of service. Thus it is very useful to be able to vary your output power without a lot of fuss - inquire specifically how the power level is adjusted. Built in meters Some transmitters have a variety of meters built in to them. It is up to you whether it is more useful to have a separate frequency counter, power meter, SWR meter, modulation monitor, etcetera. They can be useful in troubleshooting other rigs if they are not built in, but they can lead to a tangle of wires and general chaos if they are not inside the same box with the transmitter.
Signal processing Some transmitters have their signal processing built in.
In others, their signal processing takes place in the mixer, or between the mixer and the transmitter. Some will have a built in limiter, which will prevent your audio levels from going so high that you cause interference to other radio stations. This tells you how badly screwed up your antenna can be without the transmitter burning itself up. Another feature that a good transmitter may have is that it will shut itself off if it senses that the SWR is too high. This is sometimes called VSWR foldback.